Mock retired university fellows, oddly trendy it's recorded (10)

'recorded' is the definition.
(documenting is a kind of recording)

'mock retired university fellows oddly trendy' is the wordplay.
'mock' becomes 'cod' (cod can mean false or inauthentic).
'retired' says the letters should be written in reverse.
'university' becomes 'U' (abbreviation as in UMass).
'fellows' becomes 'men' (fellow can mean a man).
'oddly' indicates alternate letters (letters in the odd-numbered positions are used).
The alternating letters of 'trendy' are 'ted'.
'cod' in reverse letter order is 'doc'.
'doc'+'u'+'men'+'ted'='DOCUMENTED'

'it's' is the link.