[Solr Wiki] Update of "UserTagDesign" by MarkBennett

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The "UserTagDesign" page has been changed by MarkBennett.
The comment on this change is: Adding comments about the relevancy of a tagged field match..
http://wiki.apache.org/solr/UserTagDesign?action=diff&rev1=3&rev2=4

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  The latter looks simpler, but the former allows phrase queries to match different components of a tag
  with a single query.  A Lucene PhraseQuery across multiple fields would also work for the latter if this capability is needed.
  
+ ===== Relevancy Calculations for Tags =====
+ To leverage Relevancy calculations, you'd include the tag as part of the regular fulltext search (q), vs. just adding it as a filter (fq).
+ 
+ If multiple users have tagged a document with "lucene", then that field's density for the term will be higher, so Relevancy will also tend to be higher.  However, another document with only 1 tag, which happens to be 'lucene', will likely still rank higher than a heavily tagged document with only 40% of the tags equal to 'lucene', given Lucene's default relevancy formulas.
+ 
+ More advanced relevancy models would need more sophisticated implementations, for example perhaps a custom Similarity class.
+ 
+ 
  ===== U-delUserTag =====
    remove A10.utag="~erik#lucene"