Put point at beginning of this paragraph, mark at end.
The paragraph marked is the one that contains point or follows point.
With argument ARG, puts mark at end of a following paragraph, so that
the number of paragraphs marked equals ARG.
If ARG is negative, point is put at end of this paragraph, mark is put
at beginning of this or a previous paragraph.
Interactively (or if ALLOW-EXTEND is non-nil), if this command is
repeated or (in Transient Mark mode) if the mark is active,
it marks the next ARG paragraphs after the ones already marked.