code: function isModifyingReference(reference, index, references) {
  			var identifier = reference.identifier;
  
  			return identifier &&
  				reference.init === false &&
  				reference.isWrite() &&
  				// Destructuring assignments can have multiple default value,
  				// so possibly there are multiple writeable references for the same identifier.
  				(index === 0 || references[index - 1].identifier !== identifier
  			);
  		}
docs: Checks reference if is non initializer and writable.
  @param {Reference} reference - A reference to check.
  @param {int} index - The index of the reference in the references.
  @param {Reference[]} references - The array that the reference belongs to.
  @returns {boolean} Success/Failure
  @private