38.12.4 Displaying Faces

Here are the ways to specify which faces to use for display of text:

• With defaults. The default face is used as the ultimate default for all text. (In Emacs 19 and 20, the default face is used only when no other face is specified.)
• For a mode line or header line, the face mode-line or mode-line-inactive, or header-line, is merged in just before default.
• With text properties. A character can have a face property; if so, the faces and face attributes specified there apply. See Special Properties.

  If the character has a mouse-face property, that is used instead of the face property when the mouse is “near enough” to the character.

• With overlays. An overlay can have face and mouse-face properties too; they apply to all the text covered by the overlay.
• With a region that is active. In Transient Mark mode, the region is highlighted with the face region (see Standard Faces↗).
• With special glyphs. Each glyph can specify a particular face number. See Glyphs.

If these various sources together specify more than one face for a particular character, Emacs merges the attributes of the various faces specified. For each attribute, Emacs tries first the face of any special glyph; then the face for region highlighting, if appropriate; then the faces specified by overlays, followed by those specified by text properties, then the mode-line or mode-line-inactive or header-line face (if in a mode line or a header line), and last the default face.

When multiple overlays cover one character, an overlay with higher priority overrides those with lower priority. See Overlays.