-setftrdef or setdef 
template: pers?clnt=<name|pass>&com=setftrdef&<ftr_pattern_1>=<new_def_val_1>&...
          Order of query params is important: position of 'com'
          is not important, however updates of feature values
          are performed in the order they appear in the request.
pattern : * | name[.*], where name is a path expression
descript: updates the def value of all features matching
          the feature pattern(s) to the new def value(s).
          The new def values will affect only subsequent
          user profiles. Old profiles keep the old def values.
          If no feature in DB matches a pattern, no def value
          will be updated (200 OK will still be returned).
          If the error code 401 is returned then none
          of the features matching the request pattern(s)
          has been updated to the new def value(s).
example : pers?clnt=name|pass&com=setftrdef&the_times.politics=0&the_times.athletics=1
returns : 200 OK, 401 (fail, request error), 501 (fail, server error)
200 OK  : in this case the response body is as follows
          <?xml version="1.0"?>
          <?xml-stylesheet type="text/xsl" href="/resp_xsl/rows.xsl"?>
          <result>
          <row><num_of_rows>number of relevant rows</num_of_rows></row>
          </result>
comments: the reference to the xsl file allows to view results
          in a web browser. In case the response body is handled
          directly by an application and not by a browser, this
          reference to xsl can be ignored.