Treat the pattern as an extended regular expression, rather than as a basic regular expression.

Ignore case when matching letters.

Don't bother storing the contents of the matches-ptr array.

Treat a newline in string as dividing string into multiple lines, so that `$' can match before the newline and `^' can match after. Also, don't permit `.' to match a newline, and don't permit `[^...]' to match a newline.

Otherwise, newline acts like any other ordinary character.