Some major modes such as list-buffers and occur
construct the buffer text programmatically. The easiest way for them
to support Font Lock mode is to specify the faces of text when they
insert the text in the buffer.
The way to do this is to specify the faces in the text with the
special text property font-lock-face (see Properties with Special Meanings). When Font Lock mode is enabled, this property controls
the display, just like the face property. When Font Lock mode
is disabled, font-lock-face has no effect on the display.
It is ok for a mode to use font-lock-face for some text and
also use the normal Font Lock machinery. But if the mode does not use
the normal Font Lock machinery, it should not set the variable
font-lock-defaults. In this case the face property will
not be overridden, so using the face property could work too.
However, using font-lock-face is generally preferable as it
allows the user to control the fontification by toggling
font-lock-mode, and lets the code work regardless of whether
the mode uses Font Lock machinery or not.