The effect of the /s modifier is to change . so that it also matches a newline character (which it doesn't do by default).

The effect of the /m modifier is to change ^ and $ so they match the start and end of a line (rather than the start and end of the string).

So /s changes a single metacharacter and /m changes multiple metacharacters. That's how I remember it.

And, yes, I think that /s will solve your problem.