Hmmm ... when presented with a DOCTYPE (which of course references a URL at w3.org as its means of defining the type), does anything attempt to reach-out to the Internet to retrieve that DTD?   If it did, and failed, a timeout could occur.   I quite-honestly don’t recall ...   But, if it is “noticeably slow,” then it obviously can’t be the job of XML-parsing.   It must be “something else.”   Like this, maybe.