While fixing the mime-type validation in the query optimization code, I realized that search URLs with mime-type clauses would pass through to the query engine. A quick test of msearch proves it. It looks like someone's good efforts to optimize the clauses before performing the query inadvertently added a useful feature. The cause takes the form of 'mime-type type/subtype'
msearch -u 'search:[file:///]file_name contains resume & mime_type is application/pdf'
returns all the PDF files that have resume in their name.
I will add this to msearch-gui. I may need to create an option menu listing all the registered mime-types on the system, but that will be one unruly list. I planned to introduce this feature after I replaced the backend. I don't use the file open dialog, preferring to use Nautilus, but I see an application's need for a smart open-file-dialog. The file-open-dialog could use search to display all the possible files it can open. The user could restrict the list by adding additional criteria like name, emblem (keyword), or location.