One possible choice for Hamlet appearing before jolly or unknown island town (9)

'one possible choice for hamlet appearing before' is the definition.
I know nothing about this answer so I can't judge whether it can be defined by this definition.

'jolly or unknown island town' is the wordplay.
I cannot quite see how this works, but
'jolly' could be 'rm' and 'rm' is found within the answer.
'or' is within the answer.
'unknown' could be 'y' (algebra) and 'y' is found within the answer.
The remaining letters 'tobe' is a valid word which might be clued in a way I don't see.
This may be the basis of clue (or it may be nonsense).

Can you help me to learn more?