You can find information about the manner in which group expansion works by looking here.
Information about the specific applications and components used in the Group Expansion Service is shown below.
Components
Handles requests for group expansion submitted over HTTP://
Handles requests for group expansion submitted via LDAP:// (if configured)
Handles the workflow elements of group expansion
Gathers groups the groups from the Group Expansion database cache for a single user request.
Overview
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