`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 [Google Group discussion](https://groups.google.com/forum/?fromgroups#!topic/ajax-solr/TQS_EooscT4)