[dom] Consider specifying document.evaluate and document.createNSResolver (#67)

These are currently left to [DOM 3 XPath](http://www.w3.org/TR/DOM-Level-3-XPath/xpath.html). However, that spec is (a) very old, and thus wrong in a lot of ways; (b) not very large. It could maybe be subsumed and thus give implementations an actual non-crazy reference.

[XPathEvaluator.prototype.evaluate](https://www.chromestatus.com/metrics/feature/timeline/popularity/297) has ~0.7% usage and isn't going anywhere. [XPathEvaluator.prototype.createNSResolver](https://www.chromestatus.com/metrics/feature/timeline/popularity/296) has ~0.04% and so is also likely here to stay. However [XPathEvaluator.prototype.createExpression](https://www.chromestatus.com/metrics/feature/timeline/popularity/295) is at 0.001% and could probably be left out. Which is great because that means we can very likely kill XPathExpression.

Other features of the spec that don't seem to be implemented are XPathException and XPathNamespace.

According to a comment in Blink's source code, [XPathEvaluator](https://code.google.com/p/chromium/codesearch#chromium/src/third_party/WebKit/Source/core/xml/XPathEvaluator.idl&sq=package:chromium&q=xpath%20idl&l=24) has a constructor in reality, even if not in the spec.

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Reply to this email directly or view it on GitHub:
https://github.com/whatwg/dom/issues/67