Frames
******

A frame is a screen object that contains one or more Emacs windows (see Windows).  It is the kind of object called a ``window'' in the terminology of graphical environments; but we can't call it a ``window'' here, because Emacs uses that word in a different way.  In Emacs Lisp, a frame object is a Lisp object that represents a frame on the screen.  See Frame Type.

A frame initially contains a single main window and/or a minibuffer window; you can subdivide the main window vertically or horizontally into smaller windows.  See Splitting Windows.

A terminal is a display device capable of displaying one or more Emacs frames.  In Emacs Lisp, a terminal object is a Lisp object that represents a terminal.  See Terminal Type.

There are two classes of terminals: text terminals and graphical terminals.  Text terminals are non-graphics-capable displays, including xterm and other terminal emulators.  On a text terminal, each Emacs frame occupies the terminal's entire screen; although you can create additional frames and switch between them, the terminal only shows one frame at a time.  Graphical terminals, on the other hand, are managed by graphical display systems such as the X Window System, which allow Emacs to show multiple frames simultaneously on the same display.

On GNU and Unix systems, you can create additional frames on any available terminal, within a single Emacs session, regardless of whether Emacs was started on a text or graphical terminal.  Emacs can display on both graphical and text terminals simultaneously.  This comes in handy, for instance, when you connect to the same session from several remote locations.  See Multiple Terminals.

 -- Function: framep object
     This predicate returns a non-nil value if OBJECT is a frame, and nil otherwise.  For a frame, the value indicates which kind of display the frame uses:

     t
          The frame is displayed on a text terminal.

     x
          The frame is displayed on an X graphical terminal.

     w32
          The frame is displayed on a MS-Windows graphical terminal.

     ns
          The frame is displayed on a GNUstep or Macintosh Cocoa graphical terminal.

     pc
          The frame is displayed on an MS-DOS terminal.

 -- Function: frame-terminal &optional frame
     This function returns the terminal object that displays FRAME. If FRAME is nil or unspecified, it defaults to the selected frame.

 -- Function: terminal-live-p object
     This predicate returns a non-nil value if OBJECT is a terminal that is live (i.e., not deleted), and nil otherwise. For live terminals, the return value indicates what kind of frames are displayed on that terminal; the list of possible values is the same as for framep above.

Creating Frames
===============

To create a new frame, call the function make-frame.

 -- Command: make-frame &optional alist
     This function creates and returns a new frame, displaying the current buffer.

     The ALIST argument is an alist that specifies frame parameters for the new frame.  See Frame Parameters.  If you specify the terminal parameter in ALIST, the new frame is created on that terminal.  Otherwise, if you specify the window-system frame parameter in ALIST, that determines whether the frame should be displayed on a text terminal or a graphical terminal. See Window Systems.  If neither is specified, the new frame is created in the same terminal as the selected frame.

     Any parameters not mentioned in ALIST default to the values in the alist default-frame-alist (see Initial Parameters); parameters not specified there default from the X resources or its equivalent on your operating system (see X Resources (The GNU Emacs Manual)).  After the frame is created, Emacs applies any parameters listed in frame-inherited-parameters (see below) and not present in the argument, taking the values from the frame that was selected when make-frame was called.

     Note that on multi-monitor displays (see Multiple Terminals), the window manager might position the frame differently than specified by the positional parameters in ALIST (see Position Parameters).  For example, some window managers have a policy of displaying the frame on the monitor that contains the largest part of the window (a.k.a. the dominating monitor).

     This function itself does not make the new frame the selected frame. See Input Focus.  The previously selected frame remains selected. On graphical terminals, however, the windowing system may select the new frame for its own reasons.

 -- Variable: before-make-frame-hook
     A normal hook run by make-frame before it creates the frame.

 -- Variable: after-make-frame-functions
     An abnormal hook run by make-frame after it creates the frame. Each function in after-make-frame-functions receives one argument, the frame just created.

 -- Variable: frame-inherited-parameters
     This variable specifies the list of frame parameters that a newly created frame inherits from the currently selected frame.  For each parameter (a symbol) that is an element in the list and is not present in the argument to make-frame, the function sets the value of that parameter in the created frame to its value in the selected frame.

Multiple Terminals
==================

Emacs represents each terminal as a terminal object data type (see Terminal Type).  On GNU and Unix systems, Emacs can use multiple terminals simultaneously in each session.  On other systems, it can only use a single terminal.  Each terminal object has the following attributes:

  * The name of the device used by the terminal (e.g., :0.0 or /dev/tty).

  * The terminal and keyboard coding systems used on the terminal. See Terminal I/O Encoding.

  * The kind of display associated with the terminal.  This is the symbol returned by the function terminal-live-p (i.e., x, t, w32, ns, or pc).  See Frames.

  * A list of terminal parameters.  See Terminal Parameters.

There is no primitive for creating terminal objects.  Emacs creates them as needed, such as when you call make-frame-on-display (described below).

 -- Function: terminal-name &optional terminal
     This function returns the file name of the device used by TERMINAL.  If TERMINAL is omitted or nil, it defaults to the selected frame's terminal.  TERMINAL can also be a frame, meaning that frame's terminal.

 -- Function: terminal-list
     This function returns a list of all live terminal objects.

 -- Function: get-device-terminal device
     This function returns a terminal whose device name is given by DEVICE.  If DEVICE is a string, it can be either the file name of a terminal device, or the name of an X display of the form HOST:SERVER.SCREEN.  If DEVICE is a frame, this function returns that frame's terminal; nil means the selected frame.  Finally, if DEVICE is a terminal object that represents a live terminal, that terminal is returned.  The function signals an error if its argument is none of the above.

 -- Function: delete-terminal &optional terminal force
     This function deletes all frames on TERMINAL and frees the resources used by it.  It runs the abnormal hook delete-terminal-functions, passing TERMINAL as the argument to each function.

     If TERMINAL is omitted or nil, it defaults to the selected frame's terminal.  TERMINAL can also be a frame, meaning that frame's terminal.

     Normally, this function signals an error if you attempt to delete the sole active terminal, but if FORCE is non-nil, you are allowed to do so.  Emacs automatically calls this function when the last frame on a terminal is deleted (see Deleting Frames).

 -- Variable: delete-terminal-functions
     An abnormal hook run by delete-terminal.  Each function receives one argument, the TERMINAL argument passed to delete-terminal.  Due to technical details, the functions may be called either just before the terminal is deleted, or just afterwards.

A few Lisp variables are terminal-local; that is, they have a separate binding for each terminal.  The binding in effect at any time is the one for the terminal that the currently selected frame belongs to.  These variables include default-minibuffer-frame, defining-kbd-macro, last-kbd-macro, and system-key-alist.  They are always terminal-local, and can never be buffer-local (see Buffer-Local Variables).

On GNU and Unix systems, each X display is a separate graphical terminal.  When Emacs is started from within the X window system, it uses the X display specified by the DISPLAY environment variable, or by the --display option (see Initial Options (The GNU Emacs Manual)).  Emacs can connect to other X displays via the command make-frame-on-display.  Each X display has its own selected frame and its own minibuffer windows; however, only one of those frames is ``the selected frame'' at any given moment (see Input Focus).  Emacs can even connect to other text terminals, by interacting with the emacsclient program. See Emacs Server (The GNU Emacs Manual).

A single X server can handle more than one display.  Each X display has a three-part name, HOSTNAME:DISPLAYNUMBER.SCREENNUMBER.  The first part, HOSTNAME, specifies the name of the machine to which the display is physically connected.  The second part, DISPLAYNUMBER, is a zero-based number that identifies one or more monitors connected to that machine that share a common keyboard and pointing device (mouse, tablet, etc.).  The third part, SCREENNUMBER, identifies a zero-based screen number (a separate monitor) that is part of a single monitor collection on that X server. When you use two or more screens belonging to one server, Emacs knows by the similarity in their names that they share a single keyboard.

Systems that don't use the X window system, such as MS-Windows, don't support the notion of X displays, and have only one display on each host.  The display name on these systems doesn't follow the above 3-part format; for example, the display name on MS-Windows systems is a constant string w32, and exists for compatibility, so that you could pass it to functions that expect a display name.

 -- Command: make-frame-on-display display &optional parameters
     This function creates and returns a new frame on DISPLAY, taking the other frame parameters from the alist PARAMETERS. DISPLAY should be the name of an X display (a string).

     Before creating the frame, this function ensures that Emacs is ``set up'' to display graphics.  For instance, if Emacs has not processed X resources (e.g., if it was started on a text terminal), it does so at this time.  In all other respects, this function behaves like make-frame (see Creating Frames).

 -- Function: x-display-list
     This function returns a list that indicates which X displays Emacs has a connection to.  The elements of the list are strings, and each one is a display name.

 -- Function: x-open-connection display &optional xrm-string must-succeed
     This function opens a connection to the X display DISPLAY, without creating a frame on that display.  Normally, Emacs Lisp programs need not call this function, as make-frame-on-display calls it automatically.  The only reason for calling it is to check whether communication can be established with a given X display.

     The optional argument XRM-STRING, if not nil, is a string of resource names and values, in the same format used in the .Xresources file.  See X Resources (The GNU Emacs Manual).  These values apply to all Emacs frames created on this display, overriding the resource values recorded in the X server. Here's an example of what this string might look like:

          "*BorderWidth: 3\n*InternalBorder: 2\n"

     If MUST-SUCCEED is non-nil, failure to open the connection terminates Emacs.  Otherwise, it is an ordinary Lisp error.

 -- Function: x-close-connection display
     This function closes the connection to display DISPLAY.  Before you can do this, you must first delete all the frames that were open on that display (see Deleting Frames).

On some ``multi-monitor'' setups, a single X display outputs to more than one physical monitor.  You can use the functions display-monitor-attributes-list and frame-monitor-attributes to obtain information about such setups.

 -- Function: display-monitor-attributes-list &optional display
     This function returns a list of physical monitor attributes on DISPLAY, which can be a display name (a string), a terminal, or a frame; if omitted or nil, it defaults to the selected frame's display.  Each element of the list is an association list, representing the attributes of a physical monitor.  The first element corresponds to the primary monitor.  The attribute keys and values are:

     geometry
          Position of the top-left corner of the monitor's screen and its size, in pixels, as (X Y WIDTH HEIGHT).  Note that, if the monitor is not the primary monitor, some of the coordinates might be negative.

     workarea
          Position of the top-left corner and size of the work area (``usable'' space) in pixels as (X Y WIDTH HEIGHT). This may be different from geometry in that space occupied by various window manager features (docks, taskbars, etc.) may be excluded from the work area.  Whether or not such features actually subtract from the work area depends on the platform and environment. Again, if the monitor is not the primary monitor, some of the coordinates might be negative.

     mm-size
          Width and height in millimeters as (WIDTH HEIGHT)

     frames
          List of frames that this physical monitor dominates (see below).

     name
          Name of the physical monitor as STRING.

     source
          Source of the multi-monitor information as STRING; e.g., XRandr or Xinerama.

     X, Y, WIDTH, and HEIGHT are integers. name and source may be absent.

     A frame is dominated by a physical monitor when either the largest area of the frame resides in that monitor, or (if the frame does not intersect any physical monitors) that monitor is the closest to the frame.  Every (non-tooltip) frame (whether visible or not) in a graphical display is dominated by exactly one physical monitor at a time, though the frame can span multiple (or no) physical monitors.

     Here's an example of the data produced by this function on a 2-monitor display:

            (display-monitor-attributes-list)
            =>
            (((geometry 0 0 1920 1080) ;; Left-hand, primary monitor
              (workarea 0 0 1920 1050) ;; A taskbar occupies some of the height
              (mm-size 677 381)
              (name . "DISPLAY1")
              (frames #<frame emacs@host *Messages* 0x11578c0>
                      #<frame emacs@host *scratch* 0x114b838>))
             ((geometry 1920 0 1680 1050) ;; Right-hand monitor
              (workarea 1920 0 1680 1050) ;; Whole screen can be used
              (mm-size 593 370)
              (name . "DISPLAY2")
              (frames)))

 -- Function: frame-monitor-attributes &optional frame
     This function returns the attributes of the physical monitor dominating (see above) FRAME, which defaults to the selected frame.

Frame Geometry
==============

The geometry of a frame depends on the toolkit that was used to build this instance of Emacs and the terminal that displays the frame.  This chapter describes these dependencies and some of the functions to deal with them.  Note that the FRAME argument of all of these functions has to specify a live frame (see Deleting Frames).  If omitted or nil, it specifies the selected frame (see Input Focus).

Frame Layout
------------

The drawing below sketches the layout of a frame on a graphical terminal:

             <------------ Outer Frame Width ----------->
             ___________________________________________
          ^(0)  ___________ External Border __________   |
          | |  |_____________ Title Bar ______________|  |
          | | (1)_____________ Menu Bar ______________|  | ^
          | | (2)_____________ Tool Bar ______________|  | ^
          | | (3) _________ Internal Border ________  |  | ^
          | |  | |   ^                              | |  | |
          | |  | |   |                              | |  | |
     Outer  |  | | Inner                            | |  | Native
     Frame  |  | | Frame                            | |  | Frame
     Height |  | | Height                           | |  | Height
          | |  | |   |                              | |  | |
          | |  | |<--+--- Inner Frame Width ------->| |  | |
          | |  | |   |                              | |  | |
          | |  | |___v______________________________| |  | |
          | |  |___________ Internal Border __________|  | v
          v |______________ External Border _____________|
                <-------- Native Frame Width -------->

In practice not all of the areas shown in the drawing will or may be present.  The meaning of these areas is:

Outer Frame
     The outer frame is a rectangle comprising all areas shown in the drawing.  The edges of that rectangle are called the outer edges of the frame.  The outer width and outer height of the frame specify the size of that rectangle.

     The upper left corner of the outer frame (indicated by ``(0)'' in the drawing above) is the outer position or the frame.  It is specified by and settable via the left and top frame parameters (see Position Parameters) as well as the functions frame-position and set-frame-position (see Size and Position).

External Border
     The external border is part of the decorations supplied by the window manager.  It's typically used for resizing the frame with the mouse.  The external border is normally not shown on ``fullboth'' and maximized frames (see Size Parameters) and doesn't exist for text terminal frames.

     The external border should not be confused with the outer border specified by the border-width frame parameter (see Layout Parameters).  Since the outer border is usually ignored on most platforms it is not covered here.

Title Bar
     The title bar is also part of the window manager's decorations and typically displays the title of the frame (see Frame Titles) as well as buttons for minimizing, maximizing and deleting the frame.  The title bar is usually not displayed on ``fullboth'' (see Size Parameters) or tooltip frames.  Title bars don't exist for text terminal frames.

Menu Bar
     The menu bar (see Menu Bar) can be either internal (drawn by Emacs itself) or external (drawn by a toolkit).  Most builds (GTK+, Lucid, Motif and Windows) rely on an external menu bar.  NS also uses an external menu bar which, however, is not part of the outer frame. Non-toolkit builds can provide an internal menu bar.  On text terminal frames, the menu bar is part of the frame's root window (see Windows and Frames).

Tool Bar
     Like the menu bar, the tool bar (see Tool Bar) can be either internal (drawn by Emacs itself) or external (drawn by a toolkit).  The GTK+ and NS builds have the tool bar drawn by the toolkit.  The remaining builds use internal tool bars.  With GTK+ the tool bar can be located on either side of the frame, immediately outside the internal border, see below.

Native Frame
     The native frame is a rectangle located entirely within the outer frame.  It excludes the areas occupied by the external border, the title bar and any external menu or external tool bar.  The area enclosed by the native frame is sometimes also referred to as the display area of the frame.  The edges of the native frame are called the native edges of the frame.  The native width and native height of the frame specify the size of the rectangle.

     The top left corner of the native frame specifies the native position of the frame.  (1)--(3) in the drawing above indicate that position for the various builds:

       (1) non-toolkit and terminal frames

       (2) Lucid, Motif and Windows frames

       (3) GTK+ and NS frames

     Accordingly, the native height of a frame includes the height of the tool bar but not that of the menu bar (Lucid, Motif, Windows) or those of the menu bar and the tool bar (non-toolkit and text terminal frames).

     The native position of a frame is the reference position of functions that set or return the current position of the mouse (see Mouse Position) and for functions dealing with the position of windows like window-edges, window-at or coordinates-in-window-p (see Coordinates and Windows).

Internal Border
     The internal border (see Layout Parameters) is a border drawn by Emacs around the inner frame (see below).

Inner Frame
     The inner frame is the rectangle reserved for the frame's windows. It's enclosed by the internal border which, however, is not part of the inner frame.  Its edges are called the inner edges of the frame. The inner width and inner height specify the size of the rectangle.

     As a rule, the inner frame is subdivided into the frame's root window (see Windows and Frames) and the frame's minibuffer window (see Minibuffer Windows).  There are two notable exceptions to this rule: A non-minibuffer frame contains a root window only and does not contain a minibuffer window.  A minibuffer-only frame contains only a minibuffer window which also serves as that frame's root window. See Initial Parameters for how to create such frame configurations.

Text Area
     The text area of a frame is a somewhat fictitious area located entirely within the native frame.  It can be obtained by removing from the native frame any internal borders, one vertical and one horizontal scroll bar, and one left and one right fringe as specified for this frame, see Layout Parameters.

The absolute position of a frame or its edges is usually given in terms of pixels counted from an origin at position (0, 0) of the frame's display.  Note that with multiple monitors the origin does not necessarily coincide with the top left corner of the entire usable display area.  Hence the absolute outer position of a frame or the absolute positions of the edges of the outer, native or inner frame can be negative in such an environment even when that frame is completely visible.

For a frame on a graphical terminal the following function returns the sizes of the areas described above:

 -- Function: x-frame-geometry &optional frame
     This function returns geometric attributes of FRAME.  The return value is an association list of the attributes listed below.  All coordinate, height and width values are integers counting pixels.

     outer-position
          A cons of the absolute X- and Y-coordinates of the outer position of FRAME, relative to the origin at position (0, 0) of FRAME's display.

     outer-size
          A cons of the outer width and height of FRAME.

     external-border-size
          A cons of the horizontal and vertical width of FRAME's external borders as supplied by the window manager.  If the window manager doesn't supply these values, Emacs will try to guess them from the coordinates of the outer and inner frame.

     title-bar-size
          A cons of the width and height of the title bar of FRAME as supplied by the window manager or operating system.  If both of them are zero, the frame has no title bar.  If only the width is zero, Emacs was not able to retrieve the width information.

     menu-bar-external
          If non-nil, this means the menu bar is external (not part of the native frame of FRAME).

     menu-bar-size
          A cons of the width and height of the menu bar of FRAME.

     tool-bar-external
          If non-nil, this means the tool bar is external (not part of the native frame of FRAME).

     tool-bar-position
          This tells on which side the tool bar on FRAME is and can be one of left, top, right or bottom.  The only toolkit that currently supports a value other than top is GTK+.

     tool-bar-size
          A cons of the width and height of the tool bar of FRAME.

     internal-border-width
          The width of the internal border of FRAME.

The following function can be used to retrieve the edges of the outer, native and inner frame.

 -- Function: frame-edges &optional frame type
     This function returns the edges of the outer, native or inner frame of FRAME.  FRAME must be a live frame and defaults to the selected one.  The list returned has the form (LEFT TOP RIGHT BOTTOM) where all values are in pixels relative to the position (0, 0) of FRAME's display.  For terminal frames LEFT and TOP are both zero.

     Optional argument TYPE specifies the type of the edges to return: TYPE outer-edges means to return the outer edges of FRAME, native-edges (or nil) means to return its native edges and inner-edges means to return its inner edges.

     Notice that the ``pixels at the positions'' BOTTOM and RIGHT lie immediately outside the corresponding frame.  This means that if you have, for example, two side-by-side frames positioned such that the right outer edge of the frame on the left equals the left outer edge of the frame on the right, the pixels ``representing'' that edge are part of the frame on the right.

Frame Font
----------

Each frame has a default font which specifies the default character size for that frame.  This size is meant when retrieving or changing the size of a frame in terms of ``columns'' or ``lines'' (see Size Parameters).  It is also used when resizing (see Window Sizes) or splitting (see Splitting Windows) windows.

The term line height is sometimes used instead of ``default character height''.  Similarly, the term column width is used as shorthand for ``default character width''.

 -- Function: frame-char-height &optional frame
 -- Function: frame-char-width &optional frame
     These functions return the default height and width of a character in FRAME, measured in pixels.  Together, these values establish the size of the default font on FRAME.  The values depend on the choice of font for FRAME, see Font and Color Parameters.

The default font can be also set directly with the following function:

 -- Command: set-frame-font font &optional keep-size frames
     This sets the default font to FONT.  When called interactively, it prompts for the name of a font, and uses that font on the selected frame.  When called from Lisp, FONT should be a font name (a string), a font object, font entity, or a font spec.

     If the optional argument KEEP-SIZE is nil, this keeps the number of frame lines and columns fixed.  (If non-nil, the option frame-inhibit-implied-resize described in the next section will override this.)  If KEEP-SIZE is non-nil (or with a prefix argument), it tries to keep the size of the display area of the current frame fixed by adjusting the number of lines and columns.

     If the optional argument FRAMES is nil, this applies the font to the selected frame only.  If FRAMES is non-nil, it should be a list of frames to act upon, or t meaning all existing graphical frames.

Size and Position
-----------------

You can read or change the position of a frame using the frame parameters left and top (see Position Parameters) and its size using the height and width parameters (see Size Parameters).  Here are some special features for working with sizes and positions.  For all of these functions the argument FRAME must denote a live frame and defaults to the selected frame.

 -- Function: frame-position &optional Lisp_Object &optional frame
     This function returns the outer position (see Frame Layout) of FRAME in pixels.  The value is a cons giving the coordinates of the top left corner of the outer frame of FRAME relative to an origin at the position (0, 0) of the frame's display.  On a text terminal frame both values are zero.

 -- Function: set-frame-position frame X Y
     This function sets the outer frame position of FRAME to X and Y.  The latter arguments specify pixels and normally count from an origin at the position (0, 0) of FRAME's display.

     A negative parameter value positions the right edge of the outer frame by -X pixels left from the right edge of the screen or the bottom edge by -Y pixels up from the bottom edge of the screen.

     This function has no effect on text terminal frames.

 -- Function: frame-pixel-height &optional frame
 -- Function: frame-pixel-width &optional frame
     These functions return the inner height and width (the height and width of the display area, see Frame Layout) of FRAME in pixels.  For a text terminal, the results are in characters rather than pixels.

 -- Function: frame-text-height &optional frame
 -- Function: frame-text-width &optional frame
     These functions return the height and width of the text area of FRAME (see Frame Layout), measured in pixels.  For a text terminal, the results are in characters rather than pixels.

     The value returned by frame-text-height differs from that returned by frame-pixel-height by not including the heights of any internal tool bar or menu bar, the height of one horizontal scroll bar and the widths of the internal border.

     The value returned by frame-text-width differs from that returned by frame-pixel-width by not including the width of one vertical scroll bar, the widths of one left and one right fringe and the widths of the internal border.

 -- Function: frame-height &optional frame
 -- Function: frame-width &optional frame
     These functions return the height and width of the text area of FRAME, measured in units of the default font height and width of FRAME (see Frame Font).  These functions are plain shorthands for writing (frame-parameter frame 'height) and (frame-parameter frame 'width).

     If the text area of FRAME measured in pixels is not a multiple of its default font size, the values returned by these functions are rounded down to the number of characters of the default font that fully fit into the text area.

 -- User Option: frame-resize-pixelwise
     If this option is nil, a frame's size is usually rounded to a multiple of the current values of that frame's frame-char-height and frame-char-width whenever the frame is resized.  If this is non-nil, no rounding occurs, hence frame sizes can increase/decrease by one pixel.

     Setting this variable usually causes the next resize operation to pass the corresponding size hints to the window manager.  This means that this variable should be set only in a user's initial file; applications should never bind it temporarily.

     The precise meaning of a value of nil for this option depends on the toolkit used.  Dragging the external border with the mouse is done character-wise provided the window manager is willing to process the corresponding size hints.  Calling set-frame-size (see below) with arguments that do not specify the frame size as an integer multiple of its character size, however, may: be ignored, cause a rounding (GTK+), or be accepted (Lucid, Motif, MS-Windows).

     With some window managers you may have to set this to non-nil in order to make a frame appear truly ``maximized'' or ``fullscreen''.

 -- Function: set-frame-size frame width height pixelwise
     This function sets the size of the text area of FRAME, measured in terms of the canonical height and width of a character on FRAME (see Frame Font).

     The optional argument PIXELWISE non-nil means to measure the new width and height in units of pixels instead.  Note that if frame-resize-pixelwise is nil, some toolkits may refuse to fully honor the request if it does not increase/decrease the frame size to a multiple of its character size.

 -- Function: set-frame-height frame height &optional pretend pixelwise
     This function resizes the text area of FRAME to a height of HEIGHT lines.  The sizes of existing windows in FRAME are altered proportionally to fit.

     If PRETEND is non-nil, then Emacs displays HEIGHT lines of output in FRAME, but does not change its value for the actual height of the frame.  This is only useful on text terminals. Using a smaller height than the terminal actually implements may be useful to reproduce behavior observed on a smaller screen, or if the terminal malfunctions when using its whole screen.  Setting the frame height ``for real'' does not always work, because knowing the correct actual size may be necessary for correct cursor positioning on text terminals.

     The optional fourth argument PIXELWISE non-nil means that FRAME should be HEIGHT pixels high.  Note that if frame-resize-pixelwise is nil, some toolkits may refuse to fully honor the request if it does not increase/decrease the frame height to a multiple of its character height.

 -- Function: set-frame-width frame width &optional pretend pixelwise
     This function sets the width of the text area of FRAME, measured in characters.  The argument PRETEND has the same meaning as in set-frame-height.

     The optional fourth argument PIXELWISE non-nil means that FRAME should be WIDTH pixels wide.  Note that if frame-resize-pixelwise is nil, some toolkits may refuse to fully honor the request if it does not increase/decrease the frame width to a multiple of its character width.

None of these three functions will make a frame smaller than needed to display all of its windows together with their scroll bars, fringes, margins, dividers, mode and header lines.  This contrasts with requests by the window manager triggered, for example, by dragging the external border of a frame with the mouse.  Such requests are always honored by clipping, if necessary, portions that cannot be displayed at the right, bottom corner of the frame.

Implied Frame Resizing
----------------------

By default, Emacs tries to keep the number of lines and columns of a frame's text area unaltered when, for example, adding or removing the menu bar, changing the default font or setting the width of the frame's scroll bars.  This means, however, that in such case Emacs must ask the window manager to resize the outer frame in order to accommodate the size change.  Note that wrapping a menu or tool bar usually does not resize the frame's outer size, hence this will alter the number of displayed lines.

Occasionally, such implied frame resizing may be unwanted, for example, when the frame is maximized or made fullscreen (where it's turned off by default).  In other cases you can disable implied resizing with the following option:

 -- User Option: frame-inhibit-implied-resize
     If this option is nil, changing font, menu bar, tool bar, internal borders, fringes or scroll bars of a specific frame may implicitly resize the frame's display area in order to preserve the number of columns or lines the frame displays.  If this option is non-nil, no implied resizing is done.

     The value of this option can be also be a list of frame parameters.  In that case, implied resizing is inhibited when changing a parameter that appears in this list.  The frame parameters currently handled by this option are: font, font-backend, internal-border-width, menu-bar-lines and tool-bar-lines.

     Changing any of the scroll-bar-width, scroll-bar-height, vertical-scroll-bars, horizontal-scroll-bars, left-fringe and right-fringe frame parameters is handled as if the frame contained just one live window.  This means, for example, that removing vertical scroll bars on a frame containing several side by side windows will shrink the outer frame width by the width of one scroll bar provided this option is nil and keep it unchanged if this option is either t or a list containing vertical-scroll-bars.

     The default value is '(tool-bar-lines) for Lucid, Motif and Windows (which means that adding/removing a tool bar there does not change the outer frame height), nil on all other window systems including GTK+ (which means that changing any of the parameters listed above may change the size of the outer frame), and t otherwise (which means the outer frame size never changes implicitly when there's no window system support).

     Note that when a frame is not large enough to accommodate a change of any of the parameters listed above, Emacs may try to enlarge the frame even if this option is non-nil.

Frame Parameters
================

A frame has many parameters that control its appearance and behavior. Just what parameters a frame has depends on what display mechanism it uses.

Frame parameters exist mostly for the sake of graphical displays. Most frame parameters have no effect when applied to a frame on a text terminal; only the height, width, name, title, menu-bar-lines, buffer-list and buffer-predicate parameters do something special.  If the terminal supports colors, the parameters foreground-color, background-color, background-mode and display-type are also meaningful.  If the terminal supports frame transparency, the parameter alpha is also meaningful.

Access to Frame Parameters
--------------------------

These functions let you read and change the parameter values of a frame.

 -- Function: frame-parameter frame parameter
     This function returns the value of the parameter PARAMETER (a symbol) of FRAME.  If FRAME is nil, it returns the selected frame's parameter.  If FRAME has no setting for PARAMETER, this function returns nil.

 -- Function: frame-parameters &optional frame
     The function frame-parameters returns an alist listing all the parameters of FRAME and their values.  If FRAME is nil or omitted, this returns the selected frame's parameters

 -- Function: modify-frame-parameters frame alist
     This function alters the parameters of frame FRAME based on the elements of ALIST.  Each element of ALIST has the form (PARM . VALUE), where PARM is a symbol naming a parameter.  If you don't mention a parameter in ALIST, its value doesn't change.  If FRAME is nil, it defaults to the selected frame.

 -- Function: set-frame-parameter frame parm value
     This function sets the frame parameter PARM to the specified VALUE.  If FRAME is nil, it defaults to the selected frame.

 -- Function: modify-all-frames-parameters alist
     This function alters the frame parameters of all existing frames according to ALIST, then modifies default-frame-alist (and, if necessary, initial-frame-alist) to apply the same parameter values to frames that will be created henceforth.

Initial Frame Parameters
------------------------

You can specify the parameters for the initial startup frame by setting initial-frame-alist in your init file (see Init File).

 -- User Option: initial-frame-alist
     This variable's value is an alist of parameter values used when creating the initial frame.  You can set this variable to specify the appearance of the initial frame without altering subsequent frames. Each element has the form:

          (PARAMETER . VALUE)

     Emacs creates the initial frame before it reads your init file.  After reading that file, Emacs checks initial-frame-alist, and applies the parameter settings in the altered value to the already created initial frame.

     If these settings affect the frame geometry and appearance, you'll see the frame appear with the wrong ones and then change to the specified ones.  If that bothers you, you can specify the same geometry and appearance with X resources; those do take effect before the frame is created.  See X Resources (The GNU Emacs Manual).

     X resource settings typically apply to all frames.  If you want to specify some X resources solely for the sake of the initial frame, and you don't want them to apply to subsequent frames, here's how to achieve this.  Specify parameters in default-frame-alist to override the X resources for subsequent frames; then, to prevent these from affecting the initial frame, specify the same parameters in initial-frame-alist with values that match the X resources.

If these parameters include (minibuffer . nil), that indicates that the initial frame should have no minibuffer.  In this case, Emacs creates a separate minibuffer-only frame as well.

 -- User Option: minibuffer-frame-alist
     This variable's value is an alist of parameter values used when creating an initial minibuffer-only frame (i.e., the minibuffer-only frame that Emacs creates if initial-frame-alist specifies a frame with no minibuffer).

 -- User Option: default-frame-alist
     This is an alist specifying default values of frame parameters for all Emacs frames---the first frame, and subsequent frames.  When using the X Window System, you can get the same results by means of X resources in many cases.

     Setting this variable does not affect existing frames.  Furthermore, functions that display a buffer in a separate frame may override the default parameters by supplying their own parameters.

If you invoke Emacs with command-line options that specify frame appearance, those options take effect by adding elements to either initial-frame-alist or default-frame-alist.  Options which affect just the initial frame, such as --geometry and --maximized, add to initial-frame-alist; the others add to default-frame-alist.  see Command Line Arguments for Emacs Invocation (The GNU Emacs Manual).

Window Frame Parameters
-----------------------

Just what parameters a frame has depends on what display mechanism it uses.  This section describes the parameters that have special meanings on some or all kinds of terminals.  Of these, name, title, height, width, buffer-list and buffer-predicate provide meaningful information in terminal frames, and tty-color-mode is meaningful only for frames on text terminals.

Basic Parameters
................

These frame parameters give the most basic information about the frame.  title and name are meaningful on all terminals.

display
     The display on which to open this frame.  It should be a string of the form HOST:DPY.SCREEN, just like the DISPLAY environment variable.  See Multiple Terminals, for more details about display names.

display-type
     This parameter describes the range of possible colors that can be used in this frame.  Its value is color, grayscale or mono.

title
     If a frame has a non-nil title, it appears in the window system's title bar at the top of the frame, and also in the mode line of windows in that frame if mode-line-frame-identification uses %F (see %-Constructs).  This is normally the case when Emacs is not using a window system, and can only display one frame at a time.  See Frame Titles.

name
     The name of the frame.  The frame name serves as a default for the frame title, if the title parameter is unspecified or nil.  If you don't specify a name, Emacs sets the frame name automatically (see Frame Titles).

     If you specify the frame name explicitly when you create the frame, the name is also used (instead of the name of the Emacs executable) when looking up X resources for the frame.

explicit-name
     If the frame name was specified explicitly when the frame was created, this parameter will be that name.  If the frame wasn't explicitly named, this parameter will be nil.

Position Parameters
...................

Position parameters' values are normally measured in pixels, but on text terminals they count characters or lines instead.

left
     The position, in pixels, of the left (or right) edge of the frame with respect to the left (or right) edge of the screen.  The value may be:

     an integer
          A positive integer relates the left edge of the frame to the left edge of the screen.  A negative integer relates the right frame edge to the right screen edge.

     (+ POS)
          This specifies the position of the left frame edge relative to the left screen edge.  The integer POS may be positive or negative; a negative value specifies a position outside the screen or on a monitor other than the primary one (for multi-monitor displays).

     (- POS)
          This specifies the position of the right frame edge relative to the right screen edge.  The integer POS may be positive or negative; a negative value specifies a position outside the screen or on a monitor other than the primary one (for multi-monitor displays).

     Some window managers ignore program-specified positions.  If you want to be sure the position you specify is not ignored, specify a non-nil value for the user-position parameter as well.

     If the window manager refuses to align a frame at the left or top screen edge, combining position notation and user-position as in

          (modify-frame-parameters
            nil '((user-position . t) (left . (+ -4))))

     may help to override that.

top
     The screen position of the top (or bottom) edge, in pixels, with respect to the top (or bottom) edge of the screen.  It works just like left, except vertically instead of horizontally.

icon-left
     The screen position of the left edge of the frame's icon, in pixels, counting from the left edge of the screen.  This takes effect when the frame is iconified, if the window manager supports this feature.  If you specify a value for this parameter, then you must also specify a value for icon-top and vice versa.

icon-top
     The screen position of the top edge of the frame's icon, in pixels, counting from the top edge of the screen.  This takes effect when the frame is iconified, if the window manager supports this feature.

user-position
     When you create a frame and specify its screen position with the left and top parameters, use this parameter to say whether the specified position was user-specified (explicitly requested in some way by a human user) or merely program-specified (chosen by a program). A non-nil value says the position was user-specified.

     Window managers generally heed user-specified positions, and some heed program-specified positions too.  But many ignore program-specified positions, placing the window in a default fashion or letting the user place it with the mouse.  Some window managers, including twm, let the user specify whether to obey program-specified positions or ignore them.

     When you call make-frame, you should specify a non-nil value for this parameter if the values of the left and top parameters represent the user's stated preference; otherwise, use nil.

Size Parameters
...............

Frame parameters specify frame sizes in character units.  On graphical displays, the default face determines the actual pixel sizes of these character units (see Face Attributes).

height
     The height of the frame's text area (see Frame Geometry), in characters.

width
     The width of the frame's text area (see Frame Geometry), in characters.

user-size
     This does for the size parameters height and width what the user-position parameter (see user-position) does for the position parameters top and left.

fullscreen
     Specify that width, height or both shall be maximized.  The value fullwidth specifies that width shall be as wide as possible.  The value fullheight specifies that height shall be as tall as possible.  The value fullboth specifies that both the width and the height shall be set to the size of the screen.  The value maximized specifies that the frame shall be maximized.

     The difference between maximized and fullboth is that a maximized frame usually keeps its title bar and the buttons for resizing and closing the frame.  Also, maximized frames typically avoid hiding any task bar or panels displayed on the desktop.  ``Fullboth'' frames, on the other hand, usually omit the title bar and occupy the entire available screen space.

     ``Fullheight'' and ``fullwidth'' frames are more similar to maximized frames in this regard.  However, these typically display an external border which might be absent with maximized frames.  Hence the heights of maximized and fullheight frames and the widths of maximized and fullwidth frames often differ by a few pixels.

     With some window managers you may have to customize the variable frame-resize-pixelwise (see Size and Position) in order to make a frame truly appear ``maximized'' or ``fullscreen''.  Moreover, some window managers might not support smooth transition between the various fullscreen or maximization states.  Customizing the variable x-frame-normalize-before-maximize can help to overcome that.

fullscreen-restore
     This parameter specifies the desired ``fullscreen'' state of the frame after invoking the toggle-frame-fullscreen command (see Frame Commands (The GNU Emacs Manual)) in the ``fullboth'' state. Normally this parameter is installed automatically by that command when toggling the state to fullboth.  If, however, you start Emacs in the fullboth state, you have to specify the desired behavior in your initial file as, for example

          (setq default-frame-alist
              '((fullscreen . fullboth) (fullscreen-restore . fullheight)))

     This will give a new frame full height after typing in it F11 for the first time.

Layout Parameters
.................

These frame parameters enable or disable various parts of the frame, or control their sizes.

border-width
     The width in pixels of the frame's border.

internal-border-width
     The distance in pixels between text (or fringe) and the frame's border.

vertical-scroll-bars
     Whether the frame has scroll bars for vertical scrolling, and which side of the frame they should be on.  The possible values are left, right, and nil for no scroll bars.

horizontal-scroll-bars
     Whether the frame has scroll bars for horizontal scrolling (t and bottom mean yes, nil means no).

scroll-bar-width
     The width of vertical scroll bars, in pixels, or nil meaning to use the default width.

scroll-bar-height
     The height of horizontal scroll bars, in pixels, or nil meaning to use the default height.

left-fringe
right-fringe
     The default width of the left and right fringes of windows in this frame (see Fringes).  If either of these is zero, that effectively removes the corresponding fringe.

     When you use frame-parameter to query the value of either of these two frame parameters, the return value is always an integer. When using set-frame-parameter, passing a nil value imposes an actual default value of 8 pixels.

right-divider-width
     The width (thickness) reserved for the right divider (see Window Dividers) of any window on the frame, in pixels.  A value of zero means to not draw right dividers.

bottom-divider-width
     The width (thickness) reserved for the bottom divider (see Window Dividers) of any window on the frame, in pixels.  A value of zero means to not draw bottom dividers.

menu-bar-lines
     The number of lines to allocate at the top of the frame for a menu bar.  The default is 1 if Menu Bar mode is enabled, and 0 otherwise. See Menu Bars (The GNU Emacs Manual).

tool-bar-lines
     The number of lines to use for the tool bar.  The default is 1 if Tool Bar mode is enabled, and 0 otherwise.  See Tool Bars (The GNU Emacs Manual).

tool-bar-position
     The position of the tool bar.  Currently only for the GTK tool bar. Value can be one of top, bottom left, right. The default is  top.

line-spacing
     Additional space to leave below each text line, in pixels (a positive integer).  See Line Height, for more information.

Buffer Parameters
.................

These frame parameters, meaningful on all kinds of terminals, deal with which buffers have been, or should, be displayed in the frame.

minibuffer
     Whether this frame has its own minibuffer.  The value t means yes, nil means no, only means this frame is just a minibuffer.  If the value is a minibuffer window (in some other frame), the frame uses that minibuffer.

     This frame parameter takes effect when the frame is created, and can not be changed afterwards.

buffer-predicate
     The buffer-predicate function for this frame.  The function other-buffer uses this predicate (from the selected frame) to decide which buffers it should consider, if the predicate is not nil.  It calls the predicate with one argument, a buffer, once for each buffer; if the predicate returns a non-nil value, it considers that buffer.

buffer-list
     A list of buffers that have been selected in this frame, ordered most-recently-selected first.

unsplittable
     If non-nil, this frame's window is never split automatically.

Window Management Parameters
............................

The following frame parameters control various aspects of the frame's interaction with the window manager.  They have no effect on text terminals.

visibility
     The state of visibility of the frame.  There are three possibilities: nil for invisible, t for visible, and icon for iconified.  See Visibility of Frames.

auto-raise
     If non-nil, Emacs automatically raises the frame when it is selected.  Some window managers do not allow this.

auto-lower
     If non-nil, Emacs automatically lowers the frame when it is deselected.  Some window managers do not allow this.

icon-type
     The type of icon to use for this frame.  If the value is a string, that specifies a file containing a bitmap to use; nil specifies no icon (in which case the window manager decides what to show); any other non-nil value specifies the default Emacs icon.

icon-name
     The name to use in the icon for this frame, when and if the icon appears.  If this is nil, the frame's title is used.

window-id
     The ID number which the graphical display uses for this frame.  Emacs assigns this parameter when the frame is created; changing the parameter has no effect on the actual ID number.

outer-window-id
     The ID number of the outermost window-system window in which the frame exists.  As with window-id, changing this parameter has no actual effect.

wait-for-wm
     If non-nil, tell Xt to wait for the window manager to confirm geometry changes.  Some window managers, including versions of Fvwm2 and KDE, fail to confirm, so Xt hangs.  Set this to nil to prevent hanging with those window managers.

sticky
     If non-nil, the frame is visible on all virtual desktops on systems with virtual desktops.

Cursor Parameters
.................

This frame parameter controls the way the cursor looks.

cursor-type
     How to display the cursor.  Legitimate values are:

     box
          Display a filled box.  (This is the default.)

     hollow
          Display a hollow box.

     nil
          Don't display a cursor.

     bar
          Display a vertical bar between characters.

     (bar . WIDTH)
          Display a vertical bar WIDTH pixels wide between characters.

     hbar
          Display a horizontal bar.

     (hbar . HEIGHT)
          Display a horizontal bar HEIGHT pixels high.

The cursor-type frame parameter may be overridden by the variables cursor-type and cursor-in-non-selected-windows:

 -- Variable: cursor-type
     This buffer-local variable controls how the cursor looks in a selected window showing the buffer.  If its value is t, that means to use the cursor specified by the cursor-type frame parameter. Otherwise, the value should be one of the cursor types listed above, and it overrides the cursor-type frame parameter.

 -- User Option: cursor-in-non-selected-windows
     This buffer-local variable controls how the cursor looks in a window that is not selected.  It supports the same values as the cursor-type frame parameter; also, nil means don't display a cursor in nonselected windows, and t (the default) means use a standard modification of the usual cursor type (solid box becomes hollow box, and bar becomes a narrower bar).

 -- User Option: blink-cursor-alist
     This variable specifies how to blink the cursor.  Each element has the form (ON-STATE . OFF-STATE).  Whenever the cursor type equals ON-STATE (comparing using equal), the corresponding OFF-STATE specifies what the cursor looks like when it blinks ``off''.  Both ON-STATE and OFF-STATE should be suitable values for the cursor-type frame parameter.

     There are various defaults for how to blink each type of cursor, if the type is not mentioned as an ON-STATE here.  Changes in this variable do not take effect immediately, only when you specify the cursor-type frame parameter.

Font and Color Parameters
.........................

These frame parameters control the use of fonts and colors.

font-backend
     A list of symbols, specifying the font backends to use for drawing fonts in the frame, in order of priority.  On X, there are currently two available font backends: x (the X core font driver) and xft (the Xft font driver).  On MS-Windows, there are currently two available font backends: gdi and uniscribe (see Windows Fonts (The GNU Emacs Manual)).  On other systems, there is only one available font backend, so it does not make sense to modify this frame parameter.

background-mode
     This parameter is either dark or light, according to whether the background color is a light one or a dark one.

tty-color-mode
     This parameter overrides the terminal's color support as given by the system's terminal capabilities database in that this parameter's value specifies the color mode to use on a text terminal.  The value can be either a symbol or a number.  A number specifies the number of colors to use (and, indirectly, what commands to issue to produce each color).  For example, (tty-color-mode . 8) specifies use of the ANSI escape sequences for 8 standard text colors.  A value of -1 turns off color support.

     If the parameter's value is a symbol, it specifies a number through the value of tty-color-mode-alist, and the associated number is used instead.

screen-gamma
     If this is a number, Emacs performs ``gamma correction'' which adjusts the brightness of all colors.  The value should be the screen gamma of your display.

     Usual PC monitors have a screen gamma of 2.2, so color values in Emacs, and in X windows generally, are calibrated to display properly on a monitor with that gamma value.  If you specify 2.2 for screen-gamma, that means no correction is needed.  Other values request correction, designed to make the corrected colors appear on your screen the way they would have appeared without correction on an ordinary monitor with a gamma value of 2.2.

     If your monitor displays colors too light, you should specify a screen-gamma value smaller than 2.2.  This requests correction that makes colors darker.  A screen gamma value of 1.5 may give good results for LCD color displays.

alpha
     This parameter specifies the opacity of the frame, on graphical displays that support variable opacity.  It should be an integer between 0 and 100, where 0 means completely transparent and 100 means completely opaque.  It can also have a nil value, which tells Emacs not to set the frame opacity (leaving it to the window manager).

     To prevent the frame from disappearing completely from view, the variable frame-alpha-lower-limit defines a lower opacity limit. If the value of the frame parameter is less than the value of this variable, Emacs uses the latter.  By default, frame-alpha-lower-limit is 20.

     The alpha frame parameter can also be a cons cell (active . inactive), where active is the opacity of the frame when it is selected, and inactive is the opacity when it is not selected.

The following frame parameters are semi-obsolete in that they are automatically equivalent to particular face attributes of particular faces (see Standard Faces (The Emacs Manual)):

font
     The name of the font for displaying text in the frame.  This is a string, either a valid font name for your system or the name of an Emacs fontset (see Fontsets).  It is equivalent to the font attribute of the default face.

foreground-color
     The color to use for the image of a character.  It is equivalent to the :foreground attribute of the default face.

background-color
     The color to use for the background of characters.  It is equivalent to the :background attribute of the default face.

mouse-color
     The color for the mouse pointer.  It is equivalent to the :background attribute of the mouse face.

cursor-color
     The color for the cursor that shows point.  It is equivalent to the :background attribute of the cursor face.

border-color
     The color for the border of the frame.  It is equivalent to the :background attribute of the border face.

scroll-bar-foreground
     If non-nil, the color for the foreground of scroll bars.  It is equivalent to the :foreground attribute of the scroll-bar face.

scroll-bar-background
     If non-nil, the color for the background of scroll bars.  It is equivalent to the :background attribute of the scroll-bar face.

Geometry
--------

Here's how to examine the data in an X-style window geometry specification:

 -- Function: x-parse-geometry geom
     The function x-parse-geometry converts a standard X window geometry string to an alist that you can use as part of the argument to make-frame.

     The alist describes which parameters were specified in GEOM, and gives the values specified for them.  Each element looks like (PARAMETER . VALUE).  The possible PARAMETER values are left, top, width, and height.

     For the size parameters, the value must be an integer.  The position parameter names left and top are not totally accurate, because some values indicate the position of the right or bottom edges instead.  The VALUE possibilities for the position parameters are: an integer, a list (+ POS), or a list (- POS); as previously described (see Position Parameters).

     Here is an example:

          (x-parse-geometry "35x70+0-0")
               => ((height . 70) (width . 35)
                   (top - 0) (left . 0))

Terminal Parameters
===================

Each terminal has a list of associated parameters.  These terminal parameters are mostly a convenient way of storage for terminal-local variables, but some terminal parameters have a special meaning.

This section describes functions to read and change the parameter values of a terminal.  They all accept as their argument either a terminal or a frame; the latter means use that frame's terminal.  An argument of nil means the selected frame's terminal.

 -- Function: terminal-parameters &optional terminal
     This function returns an alist listing all the parameters of TERMINAL and their values.

 -- Function: terminal-parameter terminal parameter
     This function returns the value of the parameter PARAMETER (a symbol) of TERMINAL.  If TERMINAL has no setting for PARAMETER, this function returns nil.

 -- Function: set-terminal-parameter terminal parameter value
     This function sets the parameter PARM of TERMINAL to the specified VALUE, and returns the previous value of that parameter.

Here's a list of a few terminal parameters that have a special meaning:

background-mode
     The classification of the terminal's background color, either light or dark.

normal-erase-is-backspace
     Value is either 1 or 0, depending on whether normal-erase-is-backspace-mode is turned on or off on this terminal.  See DEL Does Not Delete (The Emacs Manual).

terminal-initted
     After the terminal is initialized, this is set to the terminal-specific initialization function.

tty-mode-set-strings
     When present, a list of strings containing escape sequences that Emacs will output while configuring a tty for rendering.  Emacs emits these strings only when configuring a terminal: if you want to enable a mode on a terminal that is already active (for example, while in tty-setup-hook), explicitly output the necessary escape sequence using send-string-to-terminal in addition to adding the sequence to tty-mode-set-strings.

tty-mode-reset-strings
     When present, a list of strings that undo the effects of the strings in tty-mode-set-strings.  Emacs emits these strings when exiting, deleting a terminal, or suspending itself.

Frame Titles
============

Every frame has a name parameter; this serves as the default for the frame title which window systems typically display at the top of the frame.  You can specify a name explicitly by setting the name frame property.

Normally you don't specify the name explicitly, and Emacs computes the frame name automatically based on a template stored in the variable frame-title-format.  Emacs recomputes the name each time the frame is redisplayed.

 -- Variable: frame-title-format
     This variable specifies how to compute a name for a frame when you have not explicitly specified one.  The variable's value is actually a mode line construct, just like mode-line-format, except that the %c and %l constructs are ignored.  See Mode Line Data.

 -- Variable: icon-title-format
     This variable specifies how to compute the name for an iconified frame, when you have not explicitly specified the frame title.  This title appears in the icon itself.

 -- Variable: multiple-frames
     This variable is set automatically by Emacs.  Its value is t when there are two or more frames (not counting minibuffer-only frames or invisible frames).  The default value of frame-title-format uses multiple-frames so as to put the buffer name in the frame title only when there is more than one frame.

     The value of this variable is not guaranteed to be accurate except while processing frame-title-format or icon-title-format.

Deleting Frames
===============

A live frame is one that has not been deleted.  When a frame is deleted, it is removed from its terminal display, although it may continue to exist as a Lisp object until there are no more references to it.

 -- Command: delete-frame &optional frame force
     This function deletes the frame FRAME.  Unless FRAME is a tooltip, it first runs the hook delete-frame-functions (each function gets one argument, FRAME).  By default, FRAME is the selected frame.

     A frame cannot be deleted as long as its minibuffer serves as surrogate minibuffer for another frame (see Minibuffers and Frames). Normally, you cannot delete a frame if all other frames are invisible, but if FORCE is non-nil, then you are allowed to do so.

 -- Function: frame-live-p frame
     The function frame-live-p returns non-nil if the frame FRAME has not been deleted.  The possible non-nil return values are like those of framep.  See Frames.

Some window managers provide a command to delete a window.  These work by sending a special message to the program that operates the window. When Emacs gets one of these commands, it generates a delete-frame event, whose normal definition is a command that calls the function delete-frame.  See Misc Events.

Finding All Frames
==================

 -- Function: frame-list
     This function returns a list of all the live frames, i.e., those that have not been deleted.  It is analogous to buffer-list for buffers, and includes frames on all terminals.  The list that you get is newly created, so modifying the list doesn't have any effect on the internals of Emacs.

 -- Function: visible-frame-list
     This function returns a list of just the currently visible frames. See Visibility of Frames.  Frames on text terminals always count as ``visible'', even though only the selected one is actually displayed.

 -- Function: next-frame &optional frame minibuf
     This function lets you cycle conveniently through all the frames on the current display from an arbitrary starting point.  It returns the ``next'' frame after FRAME in the cycle.  If FRAME is omitted or nil, it defaults to the selected frame (see Input Focus).

     The second argument, MINIBUF, says which frames to consider:

     nil
          Exclude minibuffer-only frames.

     visible
          Consider all visible frames.

     0
          Consider all visible or iconified frames.

     a window
          Consider only the frames using that particular window as their minibuffer.

     anything else
          Consider all frames.

 -- Function: previous-frame &optional frame minibuf
     Like next-frame, but cycles through all frames in the opposite direction.

See also next-window and previous-window, in Cyclic Window Ordering.

Minibuffers and Frames
======================

Normally, each frame has its own minibuffer window at the bottom, which is used whenever that frame is selected.  If the frame has a minibuffer, you can get it with minibuffer-window (see Definition of minibuffer-window).

However, you can also create a frame without a minibuffer.  Such a frame must use the minibuffer window of some other frame.  That other frame will serve as surrogate minibuffer frame for this frame and cannot be deleted via delete-frame (see Deleting Frames) as long as this frame is live.

When you create the frame, you can explicitly specify the minibuffer window to use (in some other frame).  If you don't, then the minibuffer is found in the frame which is the value of the variable default-minibuffer-frame.  Its value should be a frame that does have a minibuffer.

If you use a minibuffer-only frame, you might want that frame to raise when you enter the minibuffer.  If so, set the variable minibuffer-auto-raise to t.  See Raising and Lowering.

 -- Variable: default-minibuffer-frame
     This variable specifies the frame to use for the minibuffer window, by default.  It does not affect existing frames.  It is always local to the current terminal and cannot be buffer-local.  See Multiple Terminals.

Input Focus
===========

At any time, one frame in Emacs is the selected frame.  The selected window always resides on the selected frame.

When Emacs displays its frames on several terminals (see Multiple Terminals), each terminal has its own selected frame.  But only one of these is ``the selected frame'': it's the frame that belongs to the terminal from which the most recent input came.  That is, when Emacs runs a command that came from a certain terminal, the selected frame is the one of that terminal.  Since Emacs runs only a single command at any given time, it needs to consider only one selected frame at a time; this frame is what we call the selected frame in this manual.  The display on which the selected frame is shown is the selected frame's display.

 -- Function: selected-frame
     This function returns the selected frame.

Some window systems and window managers direct keyboard input to the window object that the mouse is in; others require explicit clicks or commands to shift the focus to various window objects.  Either way, Emacs automatically keeps track of which frame has the focus.  To explicitly switch to a different frame from a Lisp function, call select-frame-set-input-focus.

Lisp programs can also switch frames ``temporarily'' by calling the function select-frame.  This does not alter the window system's concept of focus; rather, it escapes from the window manager's control until that control is somehow reasserted.

When using a text terminal, only one frame can be displayed at a time on the terminal, so after a call to select-frame, the next redisplay actually displays the newly selected frame.  This frame remains selected until a subsequent call to select-frame.  Each frame on a text terminal has a number which appears in the mode line before the buffer name (see Mode Line Variables).

 -- Function: select-frame-set-input-focus frame &optional norecord
     This function selects FRAME, raises it (should it happen to be obscured by other frames) and tries to give it the X server's focus. On a text terminal, the next redisplay displays the new frame on the entire terminal screen.  The optional argument NORECORD has the same meaning as for select-frame (see below).  The return value of this function is not significant.

 -- Command: select-frame frame &optional norecord
     This function selects frame FRAME, temporarily disregarding the focus of the X server if any.  The selection of FRAME lasts until the next time the user does something to select a different frame, or until the next time this function is called.  (If you are using a window system, the previously selected frame may be restored as the selected frame after return to the command loop, because it still may have the window system's input focus.)

     The specified FRAME becomes the selected frame, and its terminal becomes the selected terminal.  This function then calls select-window as a subroutine, passing the window selected within FRAME as its first argument and NORECORD as its second argument (hence, if NORECORD is non-nil, this avoids changing the order of recently selected windows nor the buffer list).  See Selecting Windows.

     This function returns FRAME, or nil if FRAME has been deleted.

     In general, you should never use select-frame in a way that could switch to a different terminal without switching back when you're done.

Emacs cooperates with the window system by arranging to select frames as the server and window manager request.  It does so by generating a special kind of input event, called a focus event, when appropriate.  The command loop handles a focus event by calling handle-switch-frame.  See Focus Events.

 -- Command: handle-switch-frame frame
     This function handles a focus event by selecting frame FRAME.

     Focus events normally do their job by invoking this command. Don't call it for any other reason.

 -- Function: redirect-frame-focus frame &optional focus-frame
     This function redirects focus from FRAME to FOCUS-FRAME. This means that FOCUS-FRAME will receive subsequent keystrokes and events intended for FRAME.  After such an event, the value of last-event-frame will be FOCUS-FRAME.  Also, switch-frame events specifying FRAME will instead select FOCUS-FRAME.

     If FOCUS-FRAME is omitted or nil, that cancels any existing redirection for FRAME, which therefore once again receives its own events.

     One use of focus redirection is for frames that don't have minibuffers. These frames use minibuffers on other frames.  Activating a minibuffer on another frame redirects focus to that frame.  This puts the focus on the minibuffer's frame, where it belongs, even though the mouse remains in the frame that activated the minibuffer.

     Selecting a frame can also change focus redirections.  Selecting frame bar, when foo had been selected, changes any redirections pointing to foo so that they point to bar instead.  This allows focus redirection to work properly when the user switches from one frame to another using select-window.

     This means that a frame whose focus is redirected to itself is treated differently from a frame whose focus is not redirected. select-frame affects the former but not the latter.

     The redirection lasts until redirect-frame-focus is called to change it.

 -- Variable: focus-in-hook
     This is a normal hook run when an Emacs frame gains input focus.

 -- Variable: focus-out-hook
     This is a normal hook run when an Emacs frame loses input focus.

 -- User Option: focus-follows-mouse
     This option is how you inform Emacs whether the window manager transfers focus when the user moves the mouse.  Non-nil says that it does. When this is so, the command other-frame moves the mouse to a position consistent with the new selected frame.

Visibility of Frames
====================

A frame on a graphical display may be visible, invisible, or iconified.  If it is visible, its contents are displayed in the usual manner.  If it is iconified, its contents are not displayed, but there is a little icon somewhere to bring the frame back into view (some window managers refer to this state as minimized rather than iconified, but from Emacs' point of view they are the same thing).  If a frame is invisible, it is not displayed at all.

Visibility is meaningless on text terminals, since only the selected one is actually displayed in any case.

 -- Function: frame-visible-p frame
     This function returns the visibility status of frame FRAME.  The value is t if FRAME is visible, nil if it is invisible, and icon if it is iconified.

     On a text terminal, all frames are considered ``visible'' for the purposes of this function, even though only one frame is displayed. See Raising and Lowering.

 -- Command: iconify-frame &optional frame
     This function iconifies frame FRAME.  If you omit FRAME, it iconifies the selected frame.

 -- Command: make-frame-visible &optional frame
     This function makes frame FRAME visible.  If you omit FRAME, it makes the selected frame visible.  This does not raise the frame, but you can do that with raise-frame if you wish (see Raising and Lowering).

 -- Command: make-frame-invisible &optional frame force
     This function makes frame FRAME invisible.  If you omit FRAME, it makes the selected frame invisible.

     Unless FORCE is non-nil, this function refuses to make FRAME invisible if all other frames are invisible..

The visibility status of a frame is also available as a frame parameter.  You can read or change it as such.  See Management Parameters.  The user can also iconify and deiconify frames with the window manager.  This happens below the level at which Emacs can exert any control, but Emacs does provide events that you can use to keep track of such changes.  See Misc Events.

Raising and Lowering Frames
===========================

Most window systems use a desktop metaphor.  Part of this metaphor is the idea that system-level windows (e.g., Emacs frames) are stacked in a notional third dimension perpendicular to the screen surface.  Where two overlap, the one higher up covers the one underneath.  You can raise or lower a frame using the functions raise-frame and lower-frame.

 -- Command: raise-frame &optional frame
     This function raises frame FRAME (default, the selected frame). If FRAME is invisible or iconified, this makes it visible.

 -- Command: lower-frame &optional frame
     This function lowers frame FRAME (default, the selected frame).

 -- User Option: minibuffer-auto-raise
     If this is non-nil, activation of the minibuffer raises the frame that the minibuffer window is in.

On window systems, you can also enable auto-raising (on frame selection) or auto-lowering (on frame deselection) using frame parameters.  See Management Parameters.

The concept of raising and lowering frames also applies to text terminal frames.  On each text terminal, only the top frame is displayed at any one time.

 -- Function: tty-top-frame terminal
     This function returns the top frame on TERMINAL.  TERMINAL should be a terminal object, a frame (meaning that frame's terminal), or nil (meaning the selected frame's terminal).  If it does not refer to a text terminal, the return value is nil.

Frame Configurations
====================

A frame configuration records the current arrangement of frames, all their properties, and the window configuration of each one. (see Window Configurations.)

 -- Function: current-frame-configuration
     This function returns a frame configuration list that describes the current arrangement of frames and their contents.

 -- Function: set-frame-configuration configuration &optional nodelete
     This function restores the state of frames described in CONFIGURATION.  However, this function does not restore deleted frames.

     Ordinarily, this function deletes all existing frames not listed in CONFIGURATION.  But if NODELETE is non-nil, the unwanted frames are iconified instead.

Mouse Tracking
==============

Sometimes it is useful to track the mouse, which means to display something to indicate where the mouse is and move the indicator as the mouse moves.  For efficient mouse tracking, you need a way to wait until the mouse actually moves.

The convenient way to track the mouse is to ask for events to represent mouse motion.  Then you can wait for motion by waiting for an event.  In addition, you can easily handle any other sorts of events that may occur.  That is useful, because normally you don't want to track the mouse forever---only until some other event, such as the release of a button.

 -- Special Form: track-mouse body...
     This special form executes BODY, with generation of mouse motion events enabled.  Typically, BODY would use read-event to read the motion events and modify the display accordingly.  See Motion Events, for the format of mouse motion events.

     The value of track-mouse is that of the last form in BODY. You should design BODY to return when it sees the up-event that indicates the release of the button, or whatever kind of event means it is time to stop tracking.

     The track-mouse form causes Emacs to generate mouse motion events by binding the variable mouse-tracking to a non-nil value.  If that variable has the special value dragging, it additionally instructs the display engine to refrain from changing the shape of the mouse pointer.  This is desirable in Lisp programs that require mouse dragging across large portions of Emacs display, which might otherwise cause the mouse pointer to change its shape according to the display portion it hovers on (see Pointer Shape).  Therefore, Lisp programs that need the mouse pointer to retain its original shape during dragging should bind track-mouse to the value dragging at the beginning of their BODY.

The usual purpose of tracking mouse motion is to indicate on the screen the consequences of pushing or releasing a button at the current position.

In many cases, you can avoid the need to track the mouse by using the mouse-face text property (see Special Properties). That works at a much lower level and runs more smoothly than Lisp-level mouse tracking.

Mouse Position
==============

The functions mouse-position and set-mouse-position give access to the current position of the mouse.

 -- Function: mouse-position
     This function returns a description of the position of the mouse.  The value looks like (FRAME X . Y), where X and Y are integers giving the (possibly rounded) position in multiples of the default character size of FRAME (see Frame Font) relative to the native position of FRAME (see Frame Geometry).

 -- Variable: mouse-position-function
     If non-nil, the value of this variable is a function for mouse-position to call.  mouse-position calls this function just before returning, with its normal return value as the sole argument, and it returns whatever this function returns to it.

     This abnormal hook exists for the benefit of packages like xt-mouse.el that need to do mouse handling at the Lisp level.

 -- Function: set-mouse-position frame x y
     This function warps the mouse to position X, Y in frame FRAME.  The arguments X and Y are integers, giving the position in multiples of the default character size of FRAME (see Frame Font) relative to the native position of FRAME (see Frame Geometry).

     The resulting mouse position is constrained to the native frame of FRAME.  If FRAME is not visible, this function does nothing. The return value is not significant.

 -- Function: mouse-pixel-position
     This function is like mouse-position except that it returns coordinates in units of pixels rather than units of characters.

 -- Function: set-mouse-pixel-position frame x y
     This function warps the mouse like set-mouse-position except that X and Y are in units of pixels rather than units of characters.

     The resulting mouse position is not constrained to the native frame of FRAME.  If FRAME is not visible, this function does nothing. The return value is not significant.

On a graphical terminal the following two functions allow to retrieve and set the absolute position of the mouse cursor.

 -- Function: x-mouse-absolute-pixel-position
     This function returns a cons cell (X . Y) of the coordinates of the mouse cursor position in pixels, relative to a position (0, 0) of the selected frame's display.

 -- Function: x-set-mouse-absolute-pixel-position x y
     This function moves the mouse cursor to the position (X, Y). The coordinates X and Y are interpreted in pixels relative to a position (0, 0) of the selected frame's display.

The following function can tell whether the mouse cursor is currently visible on a frame:

 -- Function: frame-pointer-visible-p &optional frame
     This predicate function returns non-nil if the mouse pointer displayed on FRAME is visible; otherwise it returns nil. FRAME omitted or nil means the selected frame.  This is useful when make-pointer-invisible is set to t: it allows to know if the pointer has been hidden. See Mouse Avoidance (The Emacs Manual).

Pop-Up Menus
============

A Lisp program can pop up a menu so that the user can choose an alternative with the mouse.  On a text terminal, if the mouse is not available, the user can choose an alternative using the keyboard motion keys---C-n, C-p, or up- and down-arrow keys.

 -- Function: x-popup-menu position menu
     This function displays a pop-up menu and returns an indication of what selection the user makes.

     The argument POSITION specifies where on the screen to put the top left corner of the menu.  It can be either a mouse button event (which says to put the menu where the user actuated the button) or a list of this form:

          ((XOFFSET YOFFSET) WINDOW)

     where XOFFSET and YOFFSET are coordinates, measured in pixels, counting from the top left corner of WINDOW.  WINDOW may be a window or a frame.

     If POSITION is t, it means to use the current mouse position (or the top-left corner of the frame if the mouse is not available on a text terminal).  If POSITION is nil, it means to precompute the key binding equivalents for the keymaps specified in MENU, without actually displaying or popping up the menu.

     The argument MENU says what to display in the menu.  It can be a keymap or a list of keymaps (see Menu Keymaps).  In this case, the return value is the list of events corresponding to the user's choice. This list has more than one element if the choice occurred in a submenu.  (Note that x-popup-menu does not actually execute the command bound to that sequence of events.)  On text terminals and toolkits that support menu titles, the title is taken from the prompt string of MENU if MENU is a keymap, or from the prompt string of the first keymap in MENU if it is a list of keymaps (see Defining Menus).

     Alternatively, MENU can have the following form:

          (TITLE PANE1 PANE2...)

     where each pane is a list of form

          (TITLE ITEM1 ITEM2...)

     Each ITEM should be a cons cell, (LINE . VALUE), where LINE is a string and VALUE is the value to return if that LINE is chosen.  Unlike in a menu keymap, a nil VALUE does not make the menu item non-selectable. Alternatively, each ITEM can be a string rather than a cons cell; this makes a non-selectable menu item.

     If the user gets rid of the menu without making a valid choice, for instance by clicking the mouse away from a valid choice or by typing C-g, then this normally results in a quit and x-popup-menu does not return.  But if POSITION is a mouse button event (indicating that the user invoked the menu with the mouse) then no quit occurs and x-popup-menu returns nil.

Usage note: Don't use x-popup-menu to display a menu if you could do the job with a prefix key defined with a menu keymap. If you use a menu keymap to implement a menu, C-h c and C-h a can see the individual items in that menu and provide help for them. If instead you implement the menu by defining a command that calls x-popup-menu, the help facilities cannot know what happens inside that command, so they cannot give any help for the menu's items.

The menu bar mechanism, which lets you switch between submenus by moving the mouse, cannot look within the definition of a command to see that it calls x-popup-menu.  Therefore, if you try to implement a submenu using x-popup-menu, it cannot work with the menu bar in an integrated fashion.  This is why all menu bar submenus are implemented with menu keymaps within the parent menu, and never with x-popup-menu.  See Menu Bar.

If you want a menu bar submenu to have contents that vary, you should still use a menu keymap to implement it.  To make the contents vary, add a hook function to menu-bar-update-hook to update the contents of the menu keymap as necessary.

Dialog Boxes
============

A dialog box is a variant of a pop-up menu---it looks a little different, it always appears in the center of a frame, and it has just one level and one or more buttons.  The main use of dialog boxes is for asking questions that the user can answer with ``yes'', ``no'', and a few other alternatives.  With a single button, they can also force the user to acknowledge important information.  The functions y-or-n-p and yes-or-no-p use dialog boxes instead of the keyboard, when called from commands invoked by mouse clicks.

 -- Function: x-popup-dialog position contents &optional header
     This function displays a pop-up dialog box and returns an indication of what selection the user makes.  The argument CONTENTS specifies the alternatives to offer; it has this format:

          (TITLE (STRING . VALUE)...)

     which looks like the list that specifies a single pane for x-popup-menu.

     The return value is VALUE from the chosen alternative.

     As for x-popup-menu, an element of the list may be just a string instead of a cons cell (STRING . VALUE). That makes a box that cannot be selected.

     If nil appears in the list, it separates the left-hand items from the right-hand items; items that precede the nil appear on the left, and items that follow the nil appear on the right.  If you don't include a nil in the list, then approximately half the items appear on each side.

     Dialog boxes always appear in the center of a frame; the argument POSITION specifies which frame.  The possible values are as in x-popup-menu, but the precise coordinates or the individual window don't matter; only the frame matters.

     If HEADER is non-nil, the frame title for the box is Information, otherwise it is Question.  The former is used for message-box (see message-box).  (On text terminals, the box title is not displayed.)

     In some configurations, Emacs cannot display a real dialog box; so instead it displays the same items in a pop-up menu in the center of the frame.

     If the user gets rid of the dialog box without making a valid choice, for instance using the window manager, then this produces a quit and x-popup-dialog does not return.

Pointer Shape
=============

You can specify the mouse pointer style for particular text or images using the pointer text property, and for images with the :pointer and :map image properties.  The values you can use in these properties are text (or nil), arrow, hand, vdrag, hdrag, modeline, and hourglass.  text stands for the usual mouse pointer style used over text.

Over void parts of the window (parts that do not correspond to any of the buffer contents), the mouse pointer usually uses the arrow style, but you can specify a different style (one of those above) by setting void-text-area-pointer.

 -- User Option: void-text-area-pointer
     This variable specifies the mouse pointer style for void text areas. These include the areas after the end of a line or below the last line in the buffer.  The default is to use the arrow (non-text) pointer style.

When using X, you can specify what the text pointer style really looks like by setting the variable x-pointer-shape.

 -- Variable: x-pointer-shape
     This variable specifies the pointer shape to use ordinarily in the Emacs frame, for the text pointer style.

 -- Variable: x-sensitive-text-pointer-shape
     This variable specifies the pointer shape to use when the mouse is over mouse-sensitive text.

These variables affect newly created frames.  They do not normally affect existing frames; however, if you set the mouse color of a frame, that also installs the current value of those two variables. See Font and Color Parameters.

The values you can use, to specify either of these pointer shapes, are defined in the file lisp/term/x-win.el.  Use M-x apropos RET x-pointer RET to see a list of them.

Window System Selections
========================

In the X window system, data can be transferred between different applications by means of selections.  X defines an arbitrary number of selection types, each of which can store its own data; however, only three are commonly used: the clipboard, primary selection, and secondary selection.  See Cut and Paste (The GNU Emacs Manual), for Emacs commands that make use of these selections.  This section documents the low-level functions for reading and setting X selections.

 -- Command: x-set-selection type data
     This function sets an X selection.  It takes two arguments: a selection type TYPE, and the value to assign to it, DATA.

     TYPE should be a symbol; it is usually one of PRIMARY, SECONDARY or CLIPBOARD.  These are symbols with upper-case names, in accord with X Window System conventions.  If TYPE is nil, that stands for PRIMARY.

     If DATA is nil, it means to clear out the selection. Otherwise, DATA may be a string, a symbol, an integer (or a cons of two integers or list of two integers), an overlay, or a cons of two markers pointing to the same buffer.  An overlay or a pair of markers stands for text in the overlay or between the markers.  The argument DATA may also be a vector of valid non-vector selection values.

     This function returns DATA.

 -- Function: x-get-selection &optional type data-type
     This function accesses selections set up by Emacs or by other X clients.  It takes two optional arguments, TYPE and DATA-TYPE.  The default for TYPE, the selection type, is PRIMARY.

     The DATA-TYPE argument specifies the form of data conversion to use, to convert the raw data obtained from another X client into Lisp data.  Meaningful values include TEXT, STRING, UTF8_STRING, TARGETS, LENGTH, DELETE, FILE_NAME, CHARACTER_POSITION, NAME, LINE_NUMBER, COLUMN_NUMBER, OWNER_OS, HOST_NAME, USER, CLASS, ATOM, and INTEGER.  (These are symbols with upper-case names in accord with X conventions.)  The default for DATA-TYPE is STRING.

 -- User Option: selection-coding-system
     This variable specifies the coding system to use when reading and writing selections or the clipboard.  See Coding Systems.  The default is compound-text-with-extensions, which converts to the text representation that X11 normally uses.

When Emacs runs on MS-Windows, it does not implement X selections in general, but it does support the clipboard.  x-get-selection and x-set-selection on MS-Windows support the text data type only; if the clipboard holds other types of data, Emacs treats the clipboard as empty.

Drag and Drop
=============

When a user drags something from another application over Emacs, that other application expects Emacs to tell it if Emacs can handle the data that is dragged.  The variable x-dnd-test-function is used by Emacs to determine what to reply.  The default value is x-dnd-default-test-function which accepts drops if the type of the data to be dropped is present in x-dnd-known-types.  You can customize x-dnd-test-function and/or x-dnd-known-types if you want Emacs to accept or reject drops based on some other criteria.

If you want to change the way Emacs handles drop of different types or add a new type, customize x-dnd-types-alist.  This requires detailed knowledge of what types other applications use for drag and drop.

When an URL is dropped on Emacs it may be a file, but it may also be another URL type (ftp, http, etc.).  Emacs first checks dnd-protocol-alist to determine what to do with the URL.  If there is no match there and if browse-url-browser-function is an alist, Emacs looks for a match there.  If no match is found the text for the URL is inserted.  If you want to alter Emacs behavior, you can customize these variables.

Color Names
===========

A color name is text (usually in a string) that specifies a color. Symbolic names such as black, white, red, etc., are allowed; use M-x list-colors-display to see a list of defined names.  You can also specify colors numerically in forms such as #RGB and RGB:R/G/B, where R specifies the red level, G specifies the green level, and B specifies the blue level.  You can use either one, two, three, or four hex digits for R; then you must use the same number of hex digits for all G and B as well, making either 3, 6, 9 or 12 hex digits in all.  (See the documentation of the X Window System for more details about numerical RGB specification of colors.)

These functions provide a way to determine which color names are valid, and what they look like.  In some cases, the value depends on the selected frame, as described below; see Input Focus, for the meaning of the term ``selected frame''.

To read user input of color names with completion, use read-color (see read-color).

 -- Function: color-defined-p color &optional frame
     This function reports whether a color name is meaningful.  It returns t if so; otherwise, nil.  The argument FRAME says which frame's display to ask about; if FRAME is omitted or nil, the selected frame is used.

     Note that this does not tell you whether the display you are using really supports that color.  When using X, you can ask for any defined color on any kind of display, and you will get some result---typically, the closest it can do.  To determine whether a frame can really display a certain color, use color-supported-p (see below).

     This function used to be called x-color-defined-p, and that name is still supported as an alias.

 -- Function: defined-colors &optional frame
     This function returns a list of the color names that are defined and supported on frame FRAME (default, the selected frame). If FRAME does not support colors, the value is nil.

     This function used to be called x-defined-colors, and that name is still supported as an alias.

 -- Function: color-supported-p color &optional frame background-p
     This returns t if FRAME can really display the color COLOR (or at least something close to it).  If FRAME is omitted or nil, the question applies to the selected frame.

     Some terminals support a different set of colors for foreground and background.  If BACKGROUND-P is non-nil, that means you are asking whether COLOR can be used as a background; otherwise you are asking whether it can be used as a foreground.

     The argument COLOR must be a valid color name.

 -- Function: color-gray-p color &optional frame
     This returns t if COLOR is a shade of gray, as defined on FRAME's display.  If FRAME is omitted or nil, the question applies to the selected frame.  If COLOR is not a valid color name, this function returns nil.

 -- Function: color-values color &optional frame
     This function returns a value that describes what COLOR should ideally look like on FRAME.  If COLOR is defined, the value is a list of three integers, which give the amount of red, the amount of green, and the amount of blue.  Each integer ranges in principle from 0 to 65535, but some displays may not use the full range.  This three-element list is called the rgb values of the color.

     If COLOR is not defined, the value is nil.

          (color-values "black")
               => (0 0 0)
          (color-values "white")
               => (65280 65280 65280)
          (color-values "red")
               => (65280 0 0)
          (color-values "pink")
               => (65280 49152 51968)
          (color-values "hungry")
               => nil

     The color values are returned for FRAME's display.  If FRAME is omitted or nil, the information is returned for the selected frame's display.  If the frame cannot display colors, the value is nil.

     This function used to be called x-color-values, and that name is still supported as an alias.

Text Terminal Colors
====================

Text terminals usually support only a small number of colors, and the computer uses small integers to select colors on the terminal. This means that the computer cannot reliably tell what the selected color looks like; instead, you have to inform your application which small integers correspond to which colors.  However, Emacs does know the standard set of colors and will try to use them automatically.

The functions described in this section control how terminal colors are used by Emacs.

Several of these functions use or return rgb values, described in Color Names.

These functions accept a display (either a frame or the name of a terminal) as an optional argument.  We hope in the future to make Emacs support different colors on different text terminals; then this argument will specify which terminal to operate on (the default being the selected frame's terminal; see Input Focus).  At present, though, the FRAME argument has no effect.

 -- Function: tty-color-define name number &optional rgb frame
     This function associates the color name NAME with color number NUMBER on the terminal.

     The optional argument RGB, if specified, is an rgb value, a list of three numbers that specify what the color actually looks like. If you do not specify RGB, then this color cannot be used by tty-color-approximate to approximate other colors, because Emacs will not know what it looks like.

 -- Function: tty-color-clear &optional frame
     This function clears the table of defined colors for a text terminal.

 -- Function: tty-color-alist &optional frame
     This function returns an alist recording the known colors supported by a text terminal.

     Each element has the form (NAME NUMBER . RGB) or (NAME NUMBER).  Here, NAME is the color name, NUMBER is the number used to specify it to the terminal. If present, RGB is a list of three color values (for red, green, and blue) that says what the color actually looks like.

 -- Function: tty-color-approximate rgb &optional frame
     This function finds the closest color, among the known colors supported for DISPLAY, to that described by the rgb value RGB (a list of color values).  The return value is an element of tty-color-alist.

 -- Function: tty-color-translate color &optional frame
     This function finds the closest color to COLOR among the known colors supported for DISPLAY and returns its index (an integer). If the name COLOR is not defined, the value is nil.

X Resources
===========

This section describes some of the functions and variables for querying and using X resources, or their equivalent on your operating system.  See X Resources (The GNU Emacs Manual), for more information about X resources.

 -- Function: x-get-resource attribute class &optional component subclass
     The function x-get-resource retrieves a resource value from the X Window defaults database.

     Resources are indexed by a combination of a key and a class. This function searches using a key of the form INSTANCE.ATTRIBUTE (where INSTANCE is the name under which Emacs was invoked), and using Emacs.CLASS as the class.

     The optional arguments COMPONENT and SUBCLASS add to the key and the class, respectively.  You must specify both of them or neither. If you specify them, the key is INSTANCE.COMPONENT.ATTRIBUTE, and the class is Emacs.CLASS.SUBCLASS.

 -- Variable: x-resource-class
     This variable specifies the application name that x-get-resource should look up.  The default value is "Emacs".  You can examine X resources for application names other than ``Emacs'' by binding this variable to some other string, around a call to x-get-resource.

 -- Variable: x-resource-name
     This variable specifies the instance name that x-get-resource should look up.  The default value is the name Emacs was invoked with, or the value specified with the -name or -rn switches.

To illustrate some of the above, suppose that you have the line:

     xterm.vt100.background: yellow

in your X resources file (whose name is usually ~/.Xdefaults or ~/.Xresources).  Then:

     (let ((x-resource-class "XTerm") (x-resource-name "xterm"))
       (x-get-resource "vt100.background" "VT100.Background"))
          => "yellow"

     (let ((x-resource-class "XTerm") (x-resource-name "xterm"))
       (x-get-resource "background" "VT100" "vt100" "Background"))
          => "yellow"

 -- Variable: inhibit-x-resources
     If this variable is non-nil, Emacs does not look up X resources, and X resources do not have any effect when creating new frames.

Display Feature Testing
=======================

The functions in this section describe the basic capabilities of a particular display.  Lisp programs can use them to adapt their behavior to what the display can do.  For example, a program that ordinarily uses a popup menu could use the minibuffer if popup menus are not supported.

The optional argument DISPLAY in these functions specifies which display to ask the question about.  It can be a display name, a frame (which designates the display that frame is on), or nil (which refers to the selected frame's display, see Input Focus).

See Color Names, Text Terminal Colors, for other functions to obtain information about displays.

 -- Function: display-popup-menus-p &optional display
     This function returns t if popup menus are supported on DISPLAY, nil if not.  Support for popup menus requires that the mouse be available, since the menu is popped up by clicking the mouse on some portion of the Emacs display.

 -- Function: display-graphic-p &optional display
     This function returns t if DISPLAY is a graphic display capable of displaying several frames and several different fonts at once.  This is true for displays that use a window system such as X, and false for text terminals.

 -- Function: display-mouse-p &optional display
     This function returns t if DISPLAY has a mouse available, nil if not.

 -- Function: display-color-p &optional display
     This function returns t if the screen is a color screen. It used to be called x-display-color-p, and that name is still supported as an alias.

 -- Function: display-grayscale-p &optional display
     This function returns t if the screen can display shades of gray. (All color displays can do this.)

 -- Function: display-supports-face-attributes-p attributes &optional display
     This function returns non-nil if all the face attributes in ATTRIBUTES are supported (see Face Attributes).

     The definition of ``supported'' is somewhat heuristic, but basically means that a face containing all the attributes in ATTRIBUTES, when merged with the default face for display, can be represented in a way that's

      1. different in appearance than the default face, and

      2. ``close in spirit'' to what the attributes specify, if not exact.

     Point (2) implies that a :weight black attribute will be satisfied by any display that can display bold, as will :foreground "yellow" as long as some yellowish color can be displayed, but :slant italic will not be satisfied by the tty display code's automatic substitution of a ``dim'' face for italic.

 -- Function: display-selections-p &optional display
     This function returns t if DISPLAY supports selections. Windowed displays normally support selections, but they may also be supported in some other cases.

 -- Function: display-images-p &optional display
     This function returns t if DISPLAY can display images. Windowed displays ought in principle to handle images, but some systems lack the support for that.  On a display that does not support images, Emacs cannot display a tool bar.

 -- Function: display-screens &optional display
     This function returns the number of screens associated with the display.

 -- Function: display-pixel-height &optional display
     This function returns the height of the screen in pixels. On a character terminal, it gives the height in characters.

     For graphical terminals, note that on ``multi-monitor'' setups this refers to the pixel height for all physical monitors associated with DISPLAY.  See Multiple Terminals.

 -- Function: display-pixel-width &optional display
     This function returns the width of the screen in pixels. On a character terminal, it gives the width in characters.

     For graphical terminals, note that on ``multi-monitor'' setups this refers to the pixel width for all physical monitors associated with DISPLAY.  See Multiple Terminals.

 -- Function: display-mm-height &optional display
     This function returns the height of the screen in millimeters, or nil if Emacs cannot get that information.

     For graphical terminals, note that on ``multi-monitor'' setups this refers to the height for all physical monitors associated with DISPLAY.  See Multiple Terminals.

 -- Function: display-mm-width &optional display
     This function returns the width of the screen in millimeters, or nil if Emacs cannot get that information.

     For graphical terminals, note that on ``multi-monitor'' setups this refers to the width for all physical monitors associated with DISPLAY.  See Multiple Terminals.

 -- User Option: display-mm-dimensions-alist
     This variable allows the user to specify the dimensions of graphical displays returned by display-mm-height and display-mm-width in case the system provides incorrect values.

 -- Function: display-backing-store &optional display
     This function returns the backing store capability of the display. Backing store means recording the pixels of windows (and parts of windows) that are not exposed, so that when exposed they can be displayed very quickly.

     Values can be the symbols always, when-mapped, or not-useful.  The function can also return nil when the question is inapplicable to a certain kind of display.

 -- Function: display-save-under &optional display
     This function returns non-nil if the display supports the SaveUnder feature.  That feature is used by pop-up windows to save the pixels they obscure, so that they can pop down quickly.

 -- Function: display-planes &optional display
     This function returns the number of planes the display supports. This is typically the number of bits per pixel. For a tty display, it is log to base two of the number of colors supported.

 -- Function: display-visual-class &optional display
     This function returns the visual class for the screen.  The value is one of the symbols static-gray (a limited, unchangeable number of grays), gray-scale (a full range of grays), static-color (a limited, unchangeable number of colors), pseudo-color (a limited number of colors), true-color (a full range of colors), and direct-color (a full range of colors).

 -- Function: display-color-cells &optional display
     This function returns the number of color cells the screen supports.

These functions obtain additional information about the window system in use where Emacs shows the specified DISPLAY.  (Their names begin with x- for historical reasons.)

 -- Function: x-server-version &optional display
     This function returns the list of version numbers of the GUI window system running on DISPLAY, such as the X server on GNU and Unix systems.  The value is a list of three integers: the major and minor version numbers of the protocol, and the distributor-specific release number of the window system software itself.  On GNU and Unix systems, these are normally the version of the X protocol and the distributor-specific release number of the X server software.  On MS-Windows, this is the version of the Windows OS.

 -- Function: x-server-vendor &optional display
     This function returns the ``vendor'' that provided the window system software (as a string).  On GNU and Unix systems this really means whoever distributes the X server.  On MS-Windows this is the vendor ID string of the Windows OS (Microsoft).

     When the developers of X labeled software distributors as ``vendors'', they showed their false assumption that no system could ever be developed and distributed noncommercially.