38.12.4 Displaying Faces

Here is how Emacs determines the face to use for displaying any given piece of text:

• If the text consists of a special glyph, the glyph can specify a particular face. See Glyphs.
• If the text lies within an active region, Emacs highlights it using the region face. See Standard Faces.
• If the text lies within an overlay with a non-nil face property, Emacs applies the face or face attributes specified by that property. If the overlay has a mouse-face property and the mouse is “near enough” to the overlay, Emacs applies the face or face attributes specified by the mouse-face property instead. See Overlay Properties.

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

• If the text contains a face or mouse-face property, Emacs applies the specified faces and face attributes. See Special Properties. (This is how Font Lock mode faces are applied. See Font Lock Mode.)
• If the text lies within the mode line of the selected window, Emacs applies the mode-line face. For the mode line of a non-selected window, Emacs applies the mode-line-inactive face. For a header line, Emacs applies the header-line face.
• If any given attribute has not been specified during the preceding steps, Emacs applies the attribute of the default face.

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 using the above order (i.e., first the face of any special glyph; then the face for region highlighting, if appropriate; then faces specified by overlays, then faces specified by text properties, then the mode-line or mode-line-inactive or header-line face, if appropriate, and finally the default face).