format-annotate-region

format-annotate-region is a compiled Lisp function in `format.el'.

(format-annotate-region FROM TO TRANSLATIONS FORMAT-FN IGNORE)

Generate annotations for text properties in the region.
Search for changes between FROM and TO, and describe them with a list of
annotations as defined by alist TRANSLATIONS and FORMAT-FN. IGNORE lists text
properties not to consider; any text properties that are neither ignored nor
listed in TRANSLATIONS are warned about.
If you actually want to modify the region, give the return value of this
function to `format-insert-annotations'.

Format of the TRANSLATIONS argument:

Each element is a list whose car is a PROPERTY, and the following
elements have the form (VALUE ANNOTATIONS...).
Whenever the property takes on the value VALUE, the annotations
(as formatted by FORMAT-FN) are inserted into the file.
When the property stops having that value, the matching negated annotation
will be inserted (it may actually be closed earlier and reopened, if
necessary, to keep proper nesting).

If VALUE is a list, then each element of the list is dealt with
separately.

If a VALUE is numeric, then it is assumed that there is a single annotation
and each occurrence of it increments the value of the property by that number.
Thus, given the entry (left-margin (4 "indent")), if the left margin
changes from 4 to 12, two <indent> annotations will be generated.

If the VALUE is nil, then instead of annotations, a function should be
specified. This function is used as a default: it is called for all
transitions not explicitly listed in the table. The function is called with
two arguments, the OLD and NEW values of the property. It should return
a cons cell (CLOSE . OPEN) as `format-annotate-single-property-change' does.

The same TRANSLATIONS structure can be used in reverse for reading files.