The &filter query parameter allows Web Search administrators to enhance searches by adding hidden, additional query details when users submit a search query. This is an enhancement over previous versions of Web Search, which required that you use JavaScript to add additional details to search queries.
The &filter query parameter works just like the &query= parameter and can be used together using the optional number (#) value. For example, if the query parameter was &query0=search_criteria, the matching filter parameter would be &filter0=additional_hidden_search_criteria. This allows the multiple weighted queries feature to work as designed while allowing administrators to add additional query details to each query.
Unlike the &query parameter, the &filter parameter can be sent multiple times. For example, if users search for software patches, you could include the various products to be searched, which could then improve search time and accuracy:
query=software patchesfilter=/Products=Product257filter=/Products=Product16filter=/Products=Product302
The resultant URL might appear as follows, but with the HTTP and domain name prefix:
&query=software+patches&filter=%2FProducts%3DProduct257&filter=%2FProducts%3DProduct16&filter=%2FProducts%3DProduct302NOTE: All &filter operators are combined using default the &operator=value, AND. Also, the default Boolean conjunction joining the various filter operators is an OR search. You can change the default Boolean conjunction by using the &filteroperator=# query parameter. The pound sign (#) here acts just like the one used in the #operator=# query parameter.