Stefan M. said:
You can use
but I’m not sure where this is documented.
Which is exactly what I was after, thanks.
The list of characters that you can slap on to the end are (cribbed from
i => case-insensitive
o => substitute only once.
x => ignores whitespace so that you can put comments in to a regex.
m => matches over multiple lines - newlines are treated as any other
And you can use combinations too, if you fancy.