UX Designer Question:

Displaying faceted-search controls on mobile devices in a ‘tray’ overlay is a new and effective way of displaying both results and filters on relatively small mobile screens.

Faceted search lets users refine a set of results by applying filters that comprehensively describe the search space. The ability to narrow down searches is invaluable for users who need to find something specific within a large content set. This type of search has become common for e-commerce/m-commerce and travel websites, as well as many different types of document and media collections.

A faceted system includes two critical elements:
Simple controls to construct sophisticated searches - providing familiar controls like drop-down menus and checkboxes with natural-language labels. This allows ordinary users to narrow down a large set of results to a smaller set that meets their exact criteria, without any knowledge of Boolean logic or query syntax.

Simultaneous display of the facet controls and the results - Showing both the filters and the results at the same time makes it easier for users to understand the relationship between the two; ideally, this is reinforced by dynamically updating the results set as soon as the user selects filter criteria.