A character argument.
Valid values are:
- 'i' = case-insensitive matching.
- 'c' = case sensitive matching.
- 'n' = the period character (match any character) can match the newline character.
- 'm' = source_string is treated as multiple lines instead of as a single line. With this option, the '^' and '$' characters apply to each line in source_string instead of the entire source_string.
- 'l' = if source_string exceeds the current maximum allowed source_string size (currently 16 MB), a NULL is returned instead of an error. This is useful for long-running queries where you do not want long strings causing an error that would make the query fail.
- 'x' = ignore whitespace.
The argument can contain more than one character. If an illegal character is specified in the match_arg parameter, an error is reported.
If match_arg is not specified, is NULL, or is empty:
- The match is case sensitive.
- A period does not match the newline character.
- source_string is treated as a single line.