Itβs not possible to limit the search results for Google Custom Search to discussion sites only. Just in case, remember that Google Custom Search to search a single website or collection of websites. If your collection is all discussion sites, this does not seem to be the purpose of Google Custom Search. However, there may be some useful workarounds / solutions.
Workaround 0
Find or create a collection of discussion sites you are interested in and create a custom search based on this. This will accomplish (almost) the same results as you.
Workaround 1
You may be able to redirect using refinement labels. This example redirects to a Google Scholar search. You can accomplish the same result using &tbm=dsc .
<CustomSearchEngine> <Title>Universities</Title> <Context> <Facet> <FacetItem title="Papers"> <Label name="papers" mode="FILTER"/> <Redirect url="http://scholar.google.com/scholar?q=$q"/> </FacetItem> </Facet> </Context> </CustomSearchEngine>
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