Accepted rule covering tense Swiss region (6)
I believe the answer is:
canton
'tense swiss region' is the definition.
'canton' can be an answer for 'region' (Canton is an example). I am not certain of the 'tense swiss' bit.
'accepted rule covering' is the wordplay.
'accepted rule' becomes 'cant' (I can't justify this - if you can you should give a lot more credence to this answer).
'covering' becomes 'on'.
'cant'+'on'='CANTON'
Can you help me to learn more?
(Other definitions for canton that I've seen before include "Swiss administrative division" , "Administrative subdivision of, eg, Switzerland" , "part of Europe" , "Administrative region in Switzerland" , "Swiss state" .)