Tooltips are small windows that display text information at the current mouse position. They activate when there is a pause in mouse movement over some significant piece of text in a window, or the mode line, or some other part of the Emacs frame such as a tool bar button or menu item.
You can toggle the use of tooltips with the command M-x
tooltip-mode. When Tooltip mode is disabled, the help text is
displayed in the echo area instead. To control the use of tooltips at
startup, customize the variable
tooltip-delay specifies how long Emacs should
wait before displaying a tooltip. For additional customization
options for displaying tooltips, use M-x customize-group
RET tooltip RET.
If Emacs is built with GTK+ support, it displays tooltips via GTK+,
using the default appearance of GTK+ tooltips. To disable this,
change the variable
If you do this, or if Emacs is built without GTK+ support, most
attributes of the tooltip text are specified by the
face, and by X resources (see X Resources).
GUD tooltips are special tooltips that show the values of variables when debugging a program with GUD. See Debugger Operation.