Qualification Oxford, say, mostly backed, following protocols? (10)

'following protocols?' is the definition.
Both the definition and answer are adjectives. Maybe there's a link between them I don't understand?

'qualification oxford say mostly backed' is the wordplay.
'qualification' becomes 'diploma' (type of academic qualification).
'oxford say' becomes 'city' (oxford is a kind of city).
'mostly' means to remove the last letter.
'backed' shows that the letters should be reversed in order.
'city' with its final letter taken away is 'cit'.
'cit' in reverse letter order is 'tic'.
'diploma'+'tic'='DIPLOMATIC'

Can you help me to learn more?