X</m> X<regex, multiline> X<regexp, multiline> X<regular expression, multiline>
Treat string as multiple lines. That is, change "^" and "$" from matching
-the start or end of line only at the left and right ends of the string to
-matching them anywhere within the string.
+the start of the string's first line and the end of its last line to
+matching the start and end of each line within the string.
=item s
X</s> X<regex, single-line> X<regexp, single-line>