These are the bit flags that you can use in the cflags operand when
compiling a regular expression with
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.