+The argument @var{prompt} is either a string to be displayed in the
+echo area as a prompt, or @code{nil}, meaning not to display a prompt.
+The argument @var{continue-echo}, if non-@code{nil}, means to echo
+this key as a continuation of the previous key.
+
+Normally any upper case event is converted to lower case if the
+original event is undefined and the lower case equivalent is defined.
+The argument @var{dont-downcase-last}, if non-@code{nil}, means do not
+convert the last event to lower case. This is appropriate for reading
+a key sequence to be defined.
+
+The argument @var{switch-frame-ok}, if non-@code{nil}, means that this
+function should process a @code{switch-frame} event if the user
+switches frames before typing anything. If the user switches frames
+in the middle of a key sequence, or at the start of the sequence but
+@var{switch-frame-ok} is @code{nil}, then the event will be put off
+until after the current key sequence.
+
+The argument @var{command-loop}, if non-@code{nil}, means that this
+key sequence is being read by something that will read commands one
+after another. It should be @code{nil} if the caller will read just
+one key sequence.