For a number of reasons (one of them my lameness) I get extremely confused when it comes whitespace and newlines in regexps.
Say for example that I want to search for an equal sign followed by any number of whitespace and newline characters.
At certain points in time I have done the following in the belief that these regexps are equivalent:
"=[\s\n]*" "=[\s-\n]*" "=[\s]*" "=[\s-]*" "=\s*" "=\s-*"
They are not.
The emacs regexp docs just manage to confuse me on this one. :-(