code: function(category, type, name, lang)
      {
          if (typeof name === 'undefined') {
             name = '';
          }
          if (typeof lang === 'undefined') {
             lang = '';
          }
          for (var i=0; i<this._identities.length; i++)
          {
              if (this._identities[i].category == category &&
                  this._identities[i].type == type &&
                  this._identities[i].name == name &&
                  this._identities[i].lang == lang)
              {
                  return false;
              }
          }
          this._identities.push({category: category, type: type, name: name, lang: lang});
          return true;
      }
docs: Function: addIdentity
  See http://xmpp.org/registrar/disco-categories.html
  Parameters:
  (String) category - category of identity (like client, automation, etc ...)
  (String) type - type of identity (like pc, web, bot , etc ...)
  (String) name - name of identity in natural language
  (String) lang - lang of name parameter
  
  Returns:
  Boolean