Overview
Purpose: View the entities across all documents, ranked by score or frequency.
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Here's a quick explanation of significance (for the record, we came up with it first!): http://www.elasticsearch.org/blog/significant-terms-aggregation/
Workspace Filtering
Another option is to filter your result set across the entire workspace, think of this as a temporary sub-query within your query results. Examples:
Entity Significance: Double click on an entity to filter, the other widgets in your workspace will populate with only the documents that contain that particular entity.