pango:font-description-merge (desc merge replace)

desc -- a pango:font-description instance
merge -- a pango:font-description instance to merge from, or nil
replace -- if true, replace fields in desc with the corresponding values from merge, even if they are already exist

Merges the fields that are set in merge into the fields in desc. If replace is false, only fields in desc that are not already set are affected. If true, then fields that are already set will be replaced as well.

If merge is nil, this function performs nothing.