code: public PropertyOwner retrieveUserProperties(String strRegistrationKey)
      {
          if ((strRegistrationKey == null) || (strRegistrationKey.length() == 0))
              return this;        // Use default user properties
          UserProperties regKey = (UserProperties)m_htRegistration.get(strRegistrationKey);
          if (regKey == null)
              regKey = new UserProperties(this, strRegistrationKey);
          regKey.bumpUseCount(+1);
          return regKey;
      }
docs: Retrieve/Create a user properties record with this lookup key.
  User properties are accessed in two ways.
  <br/>First, if you pass a null, you get the default top-level user properties (such
  as background color, fonts, etc.).
  <br/>Second, if you pass a registration key, you get a property database for that
  specific key (such as screen field default values, specific screen sizes, etc).
  @param strPropertyCode The key I'm looking up (null for the default user's properties).
  @return The UserProperties for this registration key.