Learn how to open an XML File in Excel, Word, Chrome, and Edge on a Windows computer using the methods mentioned in this post. ... 2010, and 2013 no longer support custom XML elements.

First, according to this post, Custom XML is a Word-only thing. It's not part of Excel, PowerPoint or any other Office app. Post author Stephane Rodriguez links to a couple of Microsoft-provided ...

The "supplemental" release for Office 2007 in the U.S. includes a patch, that once, installed, makes sure "Word will no longer read the Custom XML elements contained within DOCX, DOCM, or XML files.