Tooltips are special frames (see Frames) that are used to display helpful hints (a.k.a. “tips”) related to the current position of the mouse pointer. Emacs uses tooltips to display help strings about active portions of text (see Properties with Special Meanings) and about various UI elements, such as menu items (see Extended Menu Items) and tool-bar buttons (see Tool bars).
Tooltip Mode is a minor mode that enables display of tooltips. Turning off this mode causes the tooltips be displayed in the echo area. On text-mode (a.k.a. “TTY”) frames, tooltips are always displayed in the echo area.
When Emacs is built with the GTK+ toolkit or Haiku windowing support,
it by default displays tooltips using toolkit functions, and the
appearance of the tooltips is then controlled by the toolkit’s
settings. Toolkit-provided tooltips can be disabled by changing the
value of the variable use-system-tooltips to nil. The
rest of this subsection describes how to control non-toolkit tooltips,
which are presented by Emacs itself.
Tooltips are displayed in special frames called tooltip frames, which have their own frame parameters (see Frame Parameters). Unlike other frames, the default parameters for tooltip frames are stored in a special variable.
This customizable option holds the default frame parameters used for
displaying tooltips. Any font and color parameters are ignored, and the
corresponding attributes of the tooltip face are used instead.
If left or top parameters are included, they are used as
absolute frame-relative coordinates where the tooltip should be shown.
(Mouse-relative position of the tooltip can be customized using the
variables described in Tooltips in The GNU Emacs Manual.)
Note that the left and top parameters, if present,
override the values of mouse-relative offsets.
The tooltip face determines the appearance of text shown in
tooltips. It should generally use a variable-pitch font of size that
is preferably smaller than the default frame font.
This abnormal hook is a list of functions to call when Emacs needs to
display a tooltip. Each function is called with a single argument
event which is a copy of the last mouse movement event. If a
function on this list actually displays the tooltip, it should return
non-nil, and then the rest of the functions will not be
called. The default value of this variable is a single function
tooltip-help-tips.
If you write your own function to be put on the
tooltip-functions list, you may need to know the buffer of the
mouse event that triggered the tooltip display. The following
function provides that information.
This function returns the buffer over which event occurred.
Call it with the argument of the function from
tooltip-functions to obtain the buffer whose text triggered the
tooltip. Note that the event might occur not over a buffer (e.g.,
over the tool bar), in which case this function will return
nil.
Other aspects of tooltip display are controlled by several customizable settings; see Tooltips in The GNU Emacs Manual.