Refinement Filtering in the SharePoint Search URL

The refinement filter querystring is the "r" term in a search result page URL. An example of its use is

http://intranet/search/pages/phonelist.aspx?k=christchurch&r=department%3a%22Human%20Resources%22

The value of the “r” term in the querystring decodes to

Department:”Human Resources”

Some documentation (and the links generated by the refiner web part) use a “=” character, but in my experimentation it seemed that only the “:” character would return results. Further research has shown that the “:” (%3A) character denotes a “contains” comparison whereas “=”(%3D) not surprisingly means “equals” (and yet the “equals” operation does not seem to retrieve any results in my trials)