Try this pattern:
(*ANYCRLF)<title>\s*\K.+?(?=\s*<\/title>)
I'm no expert in mirc's regex functions, can you retrieve the whole match? Normally that is preferable. If it must be in a substring for retrieval with a mirc identifier, you could use:
(*ANYCRLF)<title>\s*\K(.+?)(?=\s*<\/title>)
and the sentence should be in $regml(1). As written, the pattern should also work when the tags and content are on the same line.
No need here for the multiline option. The only time you need the multiline option is when you want to use ^ to match at the beginnings of lines and/or use $ to match at ends of lines. What constitutes a "line" and what matches dot depends on the linebreak option. Since mirc is using LF by default for its linebreak option, I would suggest to include (*ANYCRLF) at the start of patterns that will work with multi-line subjects. That way carriage returns won't be treated like normal characters.
