The text between point and the mark is known as the region. Various functions operate on text delimited by point and the mark, but only those functions specifically related to the region itself are described here.
The next two functions signal an error if the mark does not
point anywhere. If Transient Mark mode is enabled and
mark-even-if-inactive is nil, they also
signal an error if the mark is inactive.
This function returns the position of the beginning of the region (as an integer). This is the position of either point or the mark, whichever is smaller.
This function returns the position of the end of the region (as an integer). This is the position of either point or the mark, whichever is larger.
Instead of using region-beginning and
region-end, a command designed to operate on a
region should normally use interactive with the
‘r’ specification to find the beginning
and end of the region. This lets other Lisp programs specify the
bounds explicitly as arguments. See Interactive
Codes.
This function returns t if Transient Mark
mode is enabled, the mark is active, and there is a valid
region in the buffer. This function is intended to be used by
commands that operate on the region, instead of on text near
point, when the mark is active.
A region is valid if it has a non-zero size, or if the
user option use-empty-active-region is
non-nil (by default, it is nil).
The function region-active-p is similar to
use-region-p, but considers all regions as
valid. In most cases, you should not use
region-active-p, since if the region is empty it
is often more appropriate to operate on point.