This document discusses custom indexing connectors in SharePoint 2013 search. It describes how to integrate external systems like Confluence, SQL, and SAP into the SharePoint search index using connectors. The key components of a custom connector are a Business Connectivity Services (BCS) model, a BCS connector, and a protocol handler. It provides an example of developing a Confluence indexing connector that uses the BCS to surface Confluence pages and other objects in SharePoint search results.