code: function(oExpression, sIdentifierName) {
                 fCountPrimaryExpression(
                     EPrimaryExpressionCategories.N_IDENTIFIER_NAMES,
                     EValuePrefixes.S_STRING + sIdentifierName);
                 return ['dot', oWalker.walk(oExpression), sIdentifierName];
               }
docs: Increments the count of the number of occurrences of the String
  value that is equivalent to the sequence of terminal symbols
  that constitute the encountered identifier name.
  @param {!TSyntacticCodeUnit} oExpression The nonterminal
  MemberExpression.
  @param {string} sIdentifierName The identifier name used as the
  property accessor.
  @return {!Array} The encountered branch of an <abbr title=
  "abstract syntax tree">AST</abbr> with its nonterminal
  MemberExpression traversed.