@node Refresh Screen
@section Refreshing the Screen
+@cindex refresh the screen
+@cindex screen refresh
The function @code{redraw-frame} clears and redisplays the entire
contents of a given frame (@pxref{Frames}). This is useful if the
@node Echo Area Customization
@subsection Echo Area Customization
+@cindex echo area customization
These variables control details of how the echo area works.
@node Warning Variables
@subsection Warning Variables
+@cindex warning variables
Programs can customize how their warnings appear by binding
the variables described in this section.
@node Warning Options
@subsection Warning Options
+@cindex warning options
These variables are used by users to control what happens
when a Lisp program reports a warning.
@node Delayed Warnings
@subsection Delayed Warnings
+@cindex delayed warnings
Sometimes, you may wish to avoid showing a warning while a command is
running, and only show it only after the end of the command. You can
@node Temporary Displays
@section Temporary Displays
+@cindex temporary display
+@cindex temporary buffer display
Temporary displays are used by Lisp programs to put output into a
buffer and then present it to the user for perusal rather than for
@node Managing Overlays
@subsection Managing Overlays
+@cindex managing overlays
+@cindex overlays, managing
This section describes the functions to create, delete and move
overlays, and to examine their contents. Overlay changes are not
@node Overlay Properties
@subsection Overlay Properties
+@cindex overlay properties
Overlay properties are like text properties in that the properties that
alter how a character is displayed can come from either source. But in
@node Finding Overlays
@subsection Searching for Overlays
+@cindex searching for overlays
+@cindex overlays, searching for
@defun overlays-at pos &optional sorted
This function returns a list of all the overlays that cover the character at
@node Size of Displayed Text
@section Size of Displayed Text
+@cindex size of text on display
+@cindex character width on display
Since not all characters have the same width, these functions let you
check the width of a character. @xref{Primitive Indent}, and
@node Defining Faces
@subsection Defining Faces
+@cindex defining faces
@cindex face spec
The usual way to define a face is through the @code{defface} macro.
@node Attribute Functions
@subsection Face Attribute Functions
+@cindex face attributes, access and modification
This section describes functions for directly accessing and
modifying the attributes of a named face.
@node Displaying Faces
@subsection Displaying Faces
+@cindex displaying faces
+@cindex face merging
When Emacs displays a given piece of text, the visual appearance of
the text may be determined by faces drawn from different sources. If
@node Face Remapping
@subsection Face Remapping
+@cindex face remapping
The variable @code{face-remapping-alist} is used for buffer-local or
global changes in the appearance of a face. For instance, it is used
@node Basic Faces
@subsection Basic Faces
+@cindex basic faces
If your Emacs Lisp program needs to assign some faces to text, it is
often a good idea to use certain existing faces or inherit from them,
@node Font Lookup
@subsection Looking Up Fonts
+@cindex font lookup
+@cindex looking up fonts
@defun x-list-fonts name &optional reference-face frame maximum width
This function returns a list of available font names that match
@node Fontsets
@subsection Fontsets
+@cindex fontset
A @dfn{fontset} is a list of fonts, each assigned to a range of
character codes. An individual font cannot display the whole range of
@item :otf
@cindex OpenType font
The font must be an OpenType font that supports these OpenType
-features, provided Emacs is compiled with support for @samp{libotf} (a
-library for performing complex text layout in certain scripts). The
-value must be a list of the form
+features, provided Emacs is compiled with a library, such as
+@samp{libotf} on GNU/Linux, that supports complex text layout for
+scripts which need that. The value must be a list of the form
@smallexample
@code{(@var{script-tag} @var{langsys-tag} @var{gsub} @var{gpos})}
consecutive wildcards in the XLFD are folded into one.
@end defun
+The following two functions return important information about a font.
+
+@defun font-info name &optional frame
+This function returns information about a font specified by its
+@var{name}, a string, as it is used on @var{frame}. If @var{frame} is
+omitted or @code{nil}, it defaults to the selected frame.
+
+The value returned by the function is a vector of the form
+@code{[@var{opened-name} @var{full-name} @var{size} @var{height}
+@var{baseline-offset} @var{relative-compose} @var{default-ascent}
+@var{max-width} @var{ascent} @var{descent} @var{space-width}
+@var{average-width} @var{filename} @var{capability}]}. Here's the
+description of each components of this vector:
+
+@table @var
+@item opened-name
+The name used to open the font, a string.
+
+@item full-name
+The full name of the font, a string.
+
+@item size
+The pixel size of the font.
+
+@item height
+The height of the font in pixels.
+
+@item baseline-offset
+The offset in pixels from the @acronym{ASCII} baseline, positive
+upward.
+
+@item relative-compose
+@itemx default-ascent
+Numbers controlling how to compose characters.
+
+@item ascent
+@itemx descent
+The ascent and descent of this font. The sum of these two numbers
+should be equal to the value of @var{height} above.
+
+@item space-width
+The width, in pixels, of the font's space character.
+
+@item average-width
+The average width of the font characters. If this is zero, Emacs uses
+the value of @var{space-width} instead, when it calculates text layout
+on display.
+
+@item filename
+The file name of the font as a string. This can be @code{nil} if the
+font back-end does not provide a way to find out the font's file name.
+
+@item capability
+A list whose first element is a symbol representing the font type, one
+of @code{x}, @code{opentype}, @code{truetype}, @code{type1},
+@code{pcf}, or @code{bdf}. For OpenType fonts, the list includes 2
+additional elements describing the @sc{gsub} and @sc{gpos} features
+supported by the font. Each of these elements is a list of the form
+@code{((@var{script} (@var{langsys} @var{feature} @dots{}) @dots{})
+@dots{})}, where @var{script} is a symbol representing an OpenType
+script tag, @var{langsys} is a symbol representing an OpenType langsys
+tag (or @code{nil}, which stands for the default langsys), and each
+@var{feature} is a symbol representing an OpenType feature tag.
+@end table
+@end defun
+
+@defun query-font font-object
+This function returns information about a @var{font-object}. (This is
+in contrast to @code{font-info}, which takes the font name, a string,
+as its argument.)
+
+The value returned by the function is a vector of the form
+@code{[@var{name} @var{filename} @var{pixel-size} @var{max-width}
+@var{ascent} @var{descent} @var{space-width} @var{average-width}
+@var{capability}]}. Here's the description of each components of this
+vector:
+
+@table @var
+@item name
+The font name, a string.
+
+@item filename
+The file name of the font as a string. This can be @code{nil} if the
+font back-end does not provide a way to find out the font's file name.
+
+@item pixel-size
+The pixel size of the font used to open the font.
+
+@item max-width
+The maximum advance width of the font.
+
+@item ascent
+@itemx descent
+The ascent and descent of this font. The sum of these two numbers
+gives the font height.
+
+@item space-width
+The width, in pixels, of the font's space character.
+
+@item average-width
+The average width of the font characters. If this is zero, Emacs uses
+the value of @var{space-width} instead, when it calculates text layout
+on display.
+
+@item capability
+A list whose first element is a symbol representing the font type, one
+of @code{x}, @code{opentype}, @code{truetype}, @code{type1},
+@code{pcf}, or @code{bdf}. For OpenType fonts, the list includes 2
+additional elements describing the @sc{gsub} and @sc{gpos} features
+supported by the font. Each of these elements is a list of the form
+@code{((@var{script} (@var{langsys} @var{feature} @dots{}) @dots{})
+@dots{})}, where @var{script} is a symbol representing an OpenType
+script tag, @var{langsys} is a symbol representing an OpenType langsys
+tag (or @code{nil}, which stands for the default langsys), and each
+@var{feature} is a symbol representing an OpenType feature tag.
+@end table
+@end defun
+
@node Fringes
@section Fringes
@cindex fringes
@node Replacing Specs
@subsection Display Specs That Replace The Text
+@cindex replacing display specs
Some kinds of display specifications specify something to display
instead of the text that has the property. These are called
@node Defining Images
@subsection Defining Images
+@cindex define image
The functions @code{create-image}, @code{defimage} and
@code{find-image} provide convenient ways to create image descriptors.
@node Showing Images
@subsection Showing Images
+@cindex show image
You can use an image descriptor by setting up the @code{display}
property yourself, but it is easier to use the functions in this
appropriate mirrored character in the reordered text. Lisp programs
can affect the mirrored display by changing this property. Again, any
such changes affect all of Emacs display.
+
+@cindex overriding bidirectional properties
+@cindex directional overrides
+@cindex LRO
+@cindex RLO
+ The bidirectional properties of characters can be overridden by
+inserting into the text special directional control characters,
+LEFT-TO-RIGHT OVERRIDE (@acronym{LRO}) and RIGHT-TO-LEFT OVERRIDE
+(@acronym{RLO}). Any characters between a @acronym{RLO} and the
+following newline or POP DIRECTIONAL FORMATTING (@acronym{PDF})
+control character, whichever comes first, will be displayed as if they
+were strong right-to-left characters, i.e.@: they will be reversed on
+display. Similarly, any characters between @acronym{LRO} and
+@acronym{PDF} or newline will display as if they were strong
+left-to-right, and will @emph{not} be reversed even if they are strong
+right-to-left characters.
+
+@cindex phishing using directional overrides
+@cindex malicious use of directional overrides
+ These overrides are useful when you want to make some text
+unaffected by the reordering algorithm, and instead directly control
+the display order. But they can also be used for malicious purposes,
+known as @dfn{phishing}. Specifically, a URL on a Web page or a link
+in an email message can be manipulated to make its visual appearance
+unrecognizable, or similar to some popular benign location, while the
+real location, interpreted by a browser in the logical order, is very
+different.
+
+ Emacs provides a primitive that applications can use to detect
+instances of text whose bidirectional properties were overridden so as
+to make a left-to-right character display as if it were a
+right-to-left character, or vise versa.
+
+@defun bidi-find-overridden-directionality from to &optional object
+This function looks at the text of the specified @var{object} between
+positions @var{from} (inclusive) and @var{to} (exclusive), and returns
+the first position where it finds a strong left-to-right character
+whose directional properties were forced to display the character as
+right-to-left, or for a strong right-to-left character that was forced
+to display as left-to-right. If it finds no such characters in the
+specified region of text, it returns @code{nil}.
+
+The optional argument @var{object} specifies which text to search, and
+defaults to the current buffer. If @var{object} is non-@code{nil}, it
+can be some other buffer, or it can be a string or a window. If it is
+a string, the function searches that string. If it is a window, the
+function searches the buffer displayed in that window. If a buffer
+whose text you want to examine is displayed in some window, we
+recommend to specify it by that window, rather than pass the buffer to
+the function. This is because telling the function about the window
+allows it to correctly account for window-specific overlays, which
+might change the result of the function if some text in the buffer is
+covered by overlays.
+@end defun
+
+@cindex copying bidirectional text, preserve visual order
+@cindex visual order, preserve when copying bidirectional text
+ When text that includes mixed right-to-left and left-to-right
+characters and bidirectional controls is copied into a different
+location, it can change its visual appearance, and also can affect the
+visual appearance of the surrounding text at destination. This is
+because reordering of bidirectional text specified by the
+@acronym{UBA} has non-trivial context-dependent effects both on the
+copied text and on the text at copy destination that will surround it.
+
+ Sometimes, a Lisp program may need to preserve the exact visual
+appearance of the copied text at destination, and of the text that
+surrounds the copy. Lisp programs can use the following function to
+achieve that effect.
+
+@defun buffer-substring-with-bidi-context start end &optional no-properties
+This function works similar to @code{buffer-substring} (@pxref{Buffer
+Contents}), but it prepends and appends to the copied text bidi
+directional control characters necessary to preserve the visual
+appearance of the text when it is inserted at another place. Optional
+argument @var{no-properties}, if non-@code{nil}, means remove the text
+properties from the copy of the text.
+@end defun