8.5.3 Extent Type

An extent specifies temporary alteration of the display appearance of a part of a buffer (or string). It contains markers delimiting a range of the buffer, plus a property list (a list whose elements are alternating property names and values). Extents are used to present parts of the buffer temporarily in a different display style. They have no read syntax, and print in hash notation, giving the buffer name and range of positions.

Extents can exist over strings as well as buffers; the primary use of this is to preserve extent and text property information as text is copied from one buffer to another or between different parts of a buffer.

Extents have no read syntax. They print in hash notation, giving the range of text they cover, the name of the buffer or string they are in, the address in core, and a summary of some of the properties attached to the extent.

(extent-at (point))
     ⇒ #<extent [51742, 51748) font-lock text-prop 0x90121e0 in buffer objects.texi>

See Extents, for how to create and use extents.

Extents are used to implement text properties. See Text Properties.