PHP: SolrQuery::addExpandFilterQuery - Manual

publicSolrQuery::addExpandFilterQuery(string$fq): SolrQuery

Overrides main filter query, determines which documents to include in the main group.

SolrQuery::setExpand() - Enables/Disables the Expand Component
SolrQuery::addExpandSortField() - Orders the documents within the expanded groups (expand.sort parameter)
SolrQuery::removeExpandSortField() - Removes an expand sort field from the expand.sort parameter
SolrQuery::setExpandRows() - Sets the number of rows to display in each group (expand.rows). Server Default 5
SolrQuery::setExpandQuery() - Sets the expand.q parameter
SolrQuery::removeExpandFilterQuery() - Removes an expand filter query

SolrQuery::addExpandFilterQuery