Need help with intent based personal assistant / chatbot

Hello all! I have spent some time working on my chatbot and it’s
working pretty well. I have a json file that stores all my intents,
but I have come across a problem that I don’t know how to solve. I
want to have an “other” tag. This tag should be called whenever the
input doesn’t match any other patterns or tags. The goal of this is
so that if no tags are matched, I have a separate set of
instructions for my program to follow in such cases. Does anyone
have any idea how I can go about this? Is there a certain pattern I
should have or what? Also, another question I have is what if a
certain pattern I have has variables in it, for example, “Play
Clocks by Coldplay”. In the case of “Play {songName} by {artist}” a
constant pattern cannot be used since the user can come up with any
combination of song names and artists. Any help is appreciated.
Thank you in advance!