"You'd better believe it!" (3)
'you'd better believe it' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for dogma that I've seen before include "Code of beliefs accepted as authoritative" , "Religious doctrine proclaimed as true without proof" , "Article of faith" , "Code of belief" , "church teaching" .)
(Other definitions for yes that I've seen before include "Positive reply" , "Oui" , "Pro vote" , "Confirmation" , "Affirmative answer" .)