Cave coming up full of rats and the like -- do not fret (5,4)
I believe the answer is:
never mind
'the like do not fret' is the definition.
I don't know anything about this answer so I cannot judge whether it can be defined by this definition.
'cave coming up full of rats' is the wordplay.
'cave' becomes 'den' (I've seen this in another clue).
'coming up' says the letters should be written in reverse (in a down clue, letters go up).
'full of' indicates putting letters inside.
'rats' becomes 'vermin' (rats are vermin).
'den' in reverse letter order is 'ned'.
'ned' placed around 'vermin' is 'NEVER MIND'.
'and' acts as a link.
Can you help me to learn more?
(Other definitions for never mind that I've seen before include "Don't worry" , "It doesn't matter" , "who cares?" , "Forget" .)