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.
Few programs need to use the region-beginning and
region-end functions. 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.)