Regexp for beginning of a line that starts OR separates paragraphs.
This regexp should match lines that separate paragraphs
and should also match lines that start a paragraph
(and are part of that paragraph).
This is matched against the text at the left margin, which is not necessarily
the beginning of the line, so it should never use "^" as an anchor. This
ensures that the paragraph functions will work equally well within a region
of text indented by a margin setting.
The variable `paragraph-separate' specifies how to distinguish
lines that start paragraphs from lines that separate them.
If the variable `use-hard-newlines' is non-nil, then only lines following a hard newline are considered to match.