Confess about papers being biased (6)
I believe the answer is:
siding
'confess about papers being biased' is the definition.
I can't tell whether this defines the answer.
'confess about papers' is the wordplay.
'confess' becomes 'sing' (sing can informally mean to talk to the police).
'about' indicates putting letters inside.
'papers' becomes 'ID' (short for identification papers).
'sing' going around 'id' is 'SIDING'.
Can you help me to learn more?
(Other definitions for siding that I've seen before include "Short stretch of railroad track used for shunting" , "Short branch line" , "passing track" , "Short stretch of railway track off the main line" , "location for shunter" .)