The link to the ECMA-376, Second Edition, Part 3 on this page https://docs.microsoft.com/en-us/office/open-xml/introduction-to-markup-compatibility is incorrect. Here is the correct link - https://www.ecma-international.org/wp-content/uploads/ECMA-376-Fifth-Edition-Part-3-Markup-Compatibility-and-Extensibility.zip.
The link to the ECMA-376, Second Edition, Part 3 on this page https://docs.microsoft.com/en-us/office/open-xml/introduction-to-markup-compatibility is incorrect.
Here is the correct link - https://www.ecma-international.org/wp-content/uploads/ECMA-376-Fifth-Edition-Part-3-Markup-Compatibility-and-Extensibility.zip.