Additional clarification, just to muddle things a little:
However, if you use the /m regex modifier, then $ (but not \Z) changes to line-based semantics and essentially says “before the next newline or at the end of the string (whichever is first).”
The choice isn't next newline or end of string and isn't whichever is first; regular leftmost/longest backtracking rules apply. So this: 
("\n" x 10) =~ /(\s+?$)\s{3}\z/m;
print length $1;

[download]
gives 7, with the $ matching before the third-to-last newline. Same results without the ?.

In reply to Re^3: The "anchor" misnomer in regexes by ysth
in thread The "anchor" misnomer in regexes by japhy

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