This controls whether to allow the site:host.domain query
syntax in a search, to limit results to a single domain.
For example, to search for the words panda bear but only on
sites in the example.com domain, enable the syntax and use the query:
panda bear site:example.com
This will return results from example.com as well as e.g.
www.example.com, but not example.com.us.
No space may appear before or after the colon, nor in the domain. A
site: clause may only be used in conjunction with other
results-producing query parameters, e.g. keywords.
A site: clause will override any value in the From this
domain box on the Advanced Search form, which uses a separate
variable (sq). For profiles that are Meta Search back-ends, if
the front-end Meta Search is using the site: syntax, all the back-ends
should have Allow site: syntax set to Y so that the
front-end's value can be passed in.
Note that a site: query requires post-processing, which may
reduce query performance. For this reason, Allow Post-Processing
(here)
must be enabled as well for such queries.