Supplier Search by Category - details behind search

Summary

What is being searched when you enter a Category Name?

Content

Please provide details as to what is being searched when you enter a category name in the Search Area of the Suppliers train stop.  Is it searching the supplier products and services information on the supplier record, past transactions, past negotiations, agreements, etc.? 

Also, it appears that the search is only using Purchasing categories, and not browsing categories. If I don't define purchasing categories in my Suppliers Products and Services category hierarchy and use only browsing categories in the hierarchy and attach those browsing categories to the suppliers, how do those suppliers get selected if I search using a purchasing category.