* Allow whitespace around predicate parts, i.e. "[a = 'text']" instead of requiring the less readable "[a='text']".

* Add support for text comparison of the current node, like "[.='text']".

Both currently raise "invalid path" exceptions. PR coming.

Is this feature already implemented in lxml? Is it a part of some wider standard?

Well, there's XPath for a standard:
https://www.w3.org/TR/xpath/

ElementPath deviates from it in its namespace syntax (it allows "{ns}tag" where XPath requires "p:tag" prefixes), but that's about it. All other differences are basically needless limitations of ElementPath.

In fact, I had noticed these two limitations in lxml, so I implemented them for the next release. And since ElementPath in ElementTree is still mostly the same as ElementPath in lxml, here's the same thing for ET.

I think the break in the loop for [.='text'] is not correct.

>>> from xml.etree import ElementTree as ET
>>> e = ET.XML('<root><a><b>text</b></a><a><b></b></a><a><b>text</b></a></root>')
>>> list(e.findall('.//a[b="text"]'))
[<Element 'a' at 0x7ffadb305d58>, <Element 'a' at 0x7ffadb305f58>]
>>> list(e.findall('.//a[.="text"]'))
[<Element 'a' at 0x7ffadb305d58>]

I expect that findall() finds all matched elements, not just the first one. Both above requests should return the same result.

Thanks for noticing. I added a test and fixed it.

New changeset 101a5e84acbab9d880e150195f23185dfb5449a9 by Serhiy Storchaka (scoder) in branch 'master':
bpo-31648: Improve ElementPath (#3835)
https://github.com/python/cpython/commit/101a5e84acbab9d880e150195f23185dfb5449a9

Thank you for your contribution Stefan! Good improvement.