I guess I've figured out the difference between regex_contains and regex_match.
regex_match has to be matched against exactly the whole line.
So if the line is "aabb", and the regex_match is "aab", this won't be a match.
Yet regex_contains would match in this case.
Another example, "\d+" won't "regex_match" "11a",
yet "regex_contains" would match.
I haven't figured out the problem of "text", I guess the problem has something related to precedence of keybinding context rules.