code: function handleAlias(that, nameAndAlias, method) {
          var tokens, id, alias;
          tokens = extractAlias(nameAndAlias);
          id = tokens.id;
          alias = tokens.alias;
          if (id === alias) {
              throw new Error('Stager.' + method + ': id equal to alias: ' +
                              nameAndAlias);
          }
          if (alias && !that.stages[id]) {
              throw new Error('Stager.' + method + ': alias is referencing ' +
                              'non-existing stage: ' + id);
          }
          if (alias && that.stages[alias]) {
              throw new Error('Stager.' + method + ': alias is not unique: ' +
                              alias);
          }
          return tokens;
      }
docs: #### handleAlias
  
  Handles stage id and alias strings
  
  Takes a string like 'stageID' or 'stageID AS alias' and return 'alias'.
  Checks that alias and stage id are different.
  
  @param {object} that Reference to Stager object
  @param {string} nameAndAlias The stage-name string
  @param {string} method The name of the method calling the validation
  
  @return {object} Object with properties id and alias (if found)
  
  @see Stager.next
  @see handleAlias
  
  @api private