Badger editor to go in for basic principles (7)
I believe the answer is:
bedrock
'basic principles' is the definition.
(bedrock can mean principles something is based on)
'badger editor to go in' is the wordplay.
'badger' becomes 'brock' (historical term for a badger).
'editor' becomes 'ed' (abbreviation).
'to go in' means one lot of letters goes inside another.
'brock' going around 'ed' is 'BEDROCK'.
'for' acts as a link.
(Other definitions for bedrock that I've seen before include "Fundamental principles" , "Basis" , "Fundamental principle" , "Solid foundation" .)