Search may be wholly step-down: moving down the top hierarchy to select a field, choosing facets one by one and selecting a term from each, repeating this for subfacets where they exist. At each step there may be a display of the number of hits in the retrieved document set, and a short selection of document descriptions from that set. This is the basic search pattern provided by the NCSU OPAC. In eBay, in contrast, there is a preliminary step-down search through its hierarchical list of product types, followed by a display of all the facets related to the chosen product type; a term in each of these can be checked, and the next display shows the items selected by that facet combination. It may be permitted to check more than one term in a facet, this being interpreted as an OR combination, so that items corresponding to all choices are displayed