https://blogs.technet.microsoft.com/markrussinovich/2006/01/...
Is ECMA that "true", I don't know. At least they document a JavaScript without "JavaScript" in its name. MS Office (2010 at least) isn't compatible with the standard text. Is there even a MS Office nowadays that's better? Also Office 2010, dispite support, is hostile to OpenDocument format - opening a document gives you warnings about legacy format and what not.
The OOXML standatisation process was very controversial and left a bad taste around MS and ECMA Switzerland: https://en.wikipedia.org/wiki/Standardization_of_Office_Open...
But in practice there's no such thing as "OOXML" - there's only what Office 2007, 2008, 2010, 2011, 2013 and 2016 happen to do. So if you want to work with the stuff, you verify everything. The standard is, like so much Microsoft documentation, best treated as based-on-a-true-story fiction with an unreliable narrator.
http://phpexcel.codeplex.com/discussions/71551
For the most part, with Word I get better compatibility in LO with the old binary formats than with OOXML. If someone sends me .docx and it looks garbled, it's easier to ask them to resave as .doc than to try to get them to produce .odt
In my opinion, the new formats are little more than XMLified representations of implementation details of how MS Office works; there is a distinct proliferation of elements that aren't purely semantic, and an awkward-but-inconsistent lack of separation of structure from presentation. But I'm not an expert on the binary formats nor the inner workings of their applications. Though my opinions remain unchanged after 9 years, in retrospect I do like that the new formats are documented by a true standards body, and are interoperable not just by reverse-engineering a closed format.
[1] http://noooxml.wikidot.com/start