Check article started within it (7)
I believe the answer is:
therein
'within it' is the definition.
I can't tell whether this defines the answer.
'check article started' is the wordplay.
'check' becomes 'rein' (both can mean to control or limit).
'article' becomes 'the' (the definite article in English).
'started' is a charade indicator (letters next to each other).
'rein' put after 'the' is 'THEREIN'.
Can you help me to learn more?
(Other definitions for therein that I've seen before include "enclosed by that place?" , "Inside that" , "in that respect" , "Neither (anag) - into that" .)