47.10 Interaction of Extents with Keyboard and Mouse Events

If an extent has the mouse-face property set, it will be highlighted when the mouse passes over it. This includes the begin-glyph, but not the end-glyph. Highlighting is accomplished by merging the extent’s face with the face or faces specified by the mouse-face property. The effect is as if a pseudo-extent with the mouse-face face were inserted after the extent in the display order (see Extent Endpoints, display order).

Variable: mouse-highlight-priority

This variable holds the priority to use when merging in the highlighting pseudo-extent. The default is 1000. This is purposely set very high so that the highlighting pseudo-extent shows up even if there are other extents with various priorities at the same location.

You can also explicitly cause an extent to be highlighted. Only one extent at a time can be highlighted in this fashion, and any other highlighted extent will be de-highlighted.

Function: highlight-extent extent &optional highlight-p

This function highlights (if highlight-p is non-nil) or de-highlights (if highlight-p is nil) extent, if extent has the mouse-face property. (Nothing happens if extent does not have the mouse-face property.)

Function: force-highlight-extent extent &optional highlight-p

This function is similar to highlight-extent but highlights or de-highlights the extent regardless of whether it has the mouse-face property.

If an extent has a keymap property, this keymap will be consulted for mouse clicks on the extent and keypresses made while point is within the extent. The behavior of mouse clicks and keystrokes not defined in the keymap is as normal for the buffer.