isEmpty, set and clear use a simple regular expression, new RegExp('^-?' + this.field + ':'), which doesn't support more complicated fq values like: {!term f=myfield}myvalue or fq=myfield:(myvalue1 myvalue2 "my value 3") or others. See http://wiki.apache.org/solr/SolrQuerySyntax#Other_built-in_useful_query_parsers
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