Originally Posted by AudioTrack
I'm presuming that 'tidy' and 'xmllint' are Linux items. They sure sound like they are.
That hadn't occurred to me. Tidy is W3C and originally checked/tidied only HTML. It's available on pretty much every platform.
xmllint is derived from the concept of the lint program originally used to verify C programs, but later derivatives now used to verify many different languages.

As I use them, they are both command-line programs, so maybe will not have been known to put GUI users. xmllint may be a unix/linux tool, though there are Windows versions around. I know not how well they work. In principle they're both pretty much text-processing only, though xmllint may want to open schema files from the Internet.

IIRC there's a GUI Lint, but I find the command line version quicker to use than I imagine a GUI would be. There's an option for it in VisualStudio.

In principle the schema is publicly accessible and should be on musicxml.org or w3.org. It can be downloaded from the latter and should(!) be accessible from either or both, but presently may not be. I suspect most parsers and builders have local copies for performance and robustness. It's supposed to be accessible at the URI in the DOCTYPE statement, but that's musicxml.org/dtds/partwise.dtd and it's not there. partwise.dtd is also now deprecated. (See how messy this all is?).

Jazz relative beginner, starting at a much older age than was helpful.
AVL:MXE Linux; Windows 11
BIAB2025 Audiophile, a bunch of other software.
Kawai MP6, Ui24R, Focusrite Saffire Pro40 and Scarletts
.