(PECL solr >= 0.9.2)
SolrQuery::setMltMinDocFrequency — Sets the mltMinDoc frequency
The frequency at which words will be ignored which do not occur in at least this many docs.
minDocFrequencySets the frequency at which words will be ignored which do not occur in at least this many docs.
Returns the current SolrQuery object, if the return value is used.