code: function addonsManager_getSearchFilterValue(aSpec) {
      var spec = aSpec || { };
      var filter = spec.filter;
  
      if (!filter)
        throw new Error(arguments.callee.name + ": Search filter not specified.");
  
      return filter.getNode().value;
    }
docs: Get the value of the given search filter element
  
  @param {object} aSpec
  Information for getting the views matched by the criteria
  Elements: filter - Filter element
  
  @returns Value of the search filter
  @type {string}