Flags for POSIX Regular Expressions
-----------------------------------
These are the bit flags that you can use in the CFLAGS operand when
compiling a regular expression with `regcomp'.
`REG_EXTENDED'
Treat the pattern as an extended regular expression, rather than
as a basic regular expression.
`REG_ICASE'
Ignore case when matching letters.
`REG_NOSUB'
Don't bother storing the contents of the MATCHES-PTR array.
`REG_NEWLINE'
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.