It's decorative and there's nothing to add, perhaps (4)
I believe the answer is:
dado
'it's decorative and' is the definition.
I can't tell whether this defines the answer.
'nothing to add perhaps' is the wordplay.
'nothing' becomes 'O' (O resembles 0).
'perhaps' indicates anagramming the letters.
'o'+'add'='oadd'
'oadd' anagrammed gives 'DADO'.
'there's' is the link.
Can you help me to learn more?
(Other definitions for dado that I've seen before include "Rail fixed to a wall" , "Lower section of wall in room" , "Panelled lower part of a wall" , "Decorated lower part of an interior wall" , "Architectural feature" .)