Automattic/engine.io-client — pull request #341 by yujiosaka (2014-09-04 09:00:20+00:00)
Title: IE10 should prefer using XHR2 over XDR because it's safer

IE10 supports both XMLHttpRequest Level2 and XDomainRequest.
When enablesXDR option is set true, it tries to use XDR first. However, it should prefer XHR2 to XDR because XHR2 does not have such issues as not sending cookies, etc.