If a keyword search returns too many results, there are a few ways to narrow down the list further.
By Folder/Group:
Click on a Group or Folder in the Library Tree to run a search that focuses exclusively on the contents of said Group/Folder. At this time, users are able to search the contents of a single Group or Folder.
By Filter:
Open the Filters (located below the Library Tree on the left hand side panel) to apply a filter to the search results. Shelf allows users to include as many filters as they’d like to a given search query.
Keep in mind that Shelf allows you to combine keyword search, Folder/Group, and Filter at the same time for fine-grained search results.