There are a number of ways of retrieving queried data from an IWidgetContext or IResultSet.
The IWidgetContext API allows for filtering of top documents within the GUI framework, eg containing a specific set of entities (eg click on one of the bars in the graph in the "Significance" widget). This sub-set is called the filtered documents.
The IWidgetContext API lets you select which of the document sets to aggregate over.
For more information, see section Overview of Documents and Aggregations.
The following diagram provides a visual breakdown of the matching/top/filtered documents, and shows which IWidgetContext calls return data from which documents.