Flexibility outside the rules succeeded (9)

I believe the answer is:

litheness

'flexibility' is the definition.
(thesaurus)

'outside the rules succeeded' is the wordplay.
'outside' indicates putting letters inside.
'rules' becomes 'lines'.
'succeeded' becomes 's' (genealogical abbreviation).
'the' placed into 'lines' is 'lithenes'.
'lithenes'+'s'='LITHENESS'

(Another definition for litheness that I've seen is " flexibility".)

I've seen this clue in The Telegraph.

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