#### 10.3.2 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.