regex - Regular Expression Ends -

I have tried to find out in the last few hours why one of my colleagues in the world (? !!) as the last character in your regular expression instead of the usual $ .

I have noticed that there are some regular expressions: ^. * .txt (?!) that starts with Normal ^ but does not end with $ I have any definite or timely reasons I am not able to get any professional and opposition or differences?

may be < Em> end to the end of input (this depends on the modifier). Perhaps this is the reason

In my opinion, the best way to match the end of the input \ z - which means the end of the input, Regardless of the modifier. It is most supported (if not all) regex implementation