Fill paragraphs of uniform indentation within the region.
This command divides the region into "paragraphs",
treating every change in indentation level or prefix as a paragraph boundary,
then fills each paragraph using its indentation level as the fill prefix.
There is one special case where a change in indentation does not start
a new paragraph. This is for text of this form:
foo> This line with extra indentation starts
foo> a paragraph that continues on more lines.
These lines are filled together.
When calling from a program, pass the range to fill
as the first two arguments.
Optional third and fourth arguments JUSTIFY and CITATION-REGEXP:
JUSTIFY to justify paragraphs (prefix arg).
When filling a mail message, pass a regexp for CITATION-REGEXP
which will match the prefix of a line which is a citation marker
plus whitespace, but no other kind of prefix. Also, if CITATION-REGEXP is non-nil, don't fill header lines.