Where a painter might do white lines to some extent (2,1,3)
I believe the answer is:
in a way
'to some extent' is the definition.
(I've seen this in another clue)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for in a way that I've seen before include "Sort of, to a limited extent" , "Kind of" , "To some degree" , "In some respects, to a limited extent" , "From some points of view" .)