code: function(n, parent) {
  												if(n.range[1] <= start) {
  													return Estraverse.VisitorOption.Skip;
  												}
  												if(n.range[0] > end) {
  													//once we've left the parentNode
  													return Estraverse.VisitorOption.Break;
  												}
  												if (n.type === 'Identifier' && variableName === n.name && n.range[0] >= start && n.range[1] <= end) {
  													// record this reference
  													var identifierStart = n.range[0];
  													var length = n.range[1] - identifierStart;
  													groups[0].positions.push({offset: identifierStart, length: length});
  												}
  											}
docs: /* @callback