Regular Expression: DOTALL mode

Cited from DOTALL (Dot Matches Line Breaks): s (with exceptions)

"By default, the dot . doesn't match line break characters such as line feeds and carriage returns. If you want patterns such as BEGIN .*? END to match across lines, we need to turn that feature on."

"This mode is sometimes called single-line (hence the s) because as far as the dot is concerned, it turns the whole string into one big line—.* will match from the first character to the last, no matter how many line breaks stand in between."

"In Perl, apart from the (?s) inline modifier, Perl lets you add the s flag after your pattern's closing delimiter. For instance, you can use:
if ($the_subject =~ m/BEGIN .*? END/s) { … }"