Probably it’s the (JavaScript-native) object model, not the parsing? XHR appeared in IE 5 as a part of MSXML and thus had XML handling built in, and probably ev

Probably it’s the (JavaScript-native) object model, not the parsing? XHR appeared in IE 5 as a part of MSXML and thus had XML handling built in, and probably every other browser that copied it included that part as well... (not feeling up to browser archaeology at the moment, sorry). But unadorned XML DOM is just unpleasant to deal with.