You should be able to see webkit results when you browse safari or google-chrome tags.
In this case we can't use it as a synonym of both tags.
Could you implement (1) a tag complementary/correlated option or (2) a way to link several tags instead of one?
Expected result:
- webkit would redirect to (safari or google-chrome or webkit) [not and].
- safari will contain webkit unique results (not google-chrome ones)
- google-chrome will contain webkit unique results (not safari ones)
related question: Tag synonym for multiple tags