Yes, when I follow it, it now shows the "Forums" section, and it stays there if I switch to e.g. All or Web from there. It's likely encoded somewhere in the long "fbs" parameter, cause it disappears once I remove it.
But you can search forums with just udm=18. E.g. https://google.com/search?q=Foo&udm=18 -- this means you can create a custom "search with >" item for it.
But you can search forums with just udm=18. E.g. https://google.com/search?q=Foo&udm=18 -- this means you can create a custom "search with >" item for it.
Also,
6 https://www.google.com/search?q=Foo&udm=6 -- "Learn", returns mostly learning resources and references.
8 https://www.google.com/search?q=javascript+near+san+francisc... -- "Jobs", seems to use "<title> near <location>" format.
15 https://www.google.com/search?q=Foo&udm=15 -- "Attractions", seems defunct.
36 https://www.google.com/search?q=Foo&udm=36 -- "Books"
37 https://www.google.com/search?q=Foo&udm=37 -- "Products", strange one
44 https://www.google.com/search?q=Foo&udm=44 -- "Visual matches" ???
48 https://www.google.com/search?q=Foo&udm=48 -- "Exact matches" ???
51 https://www.google.com/search?q=Foo&udm=51 -- "Homework", looks like "Learn"
I guess 44, 48 is probably how image search works.