The example file in the wiki  (at https://wiki.contextgarden.net/PDF/A) no longer verifies as compliant PDF/A. VeraPDF rejects it, and https://www.pdf-online.com/osa/validate.aspx complains:

	x107.pdf
Compliance	pdfa-1b
Result	Document does not conform to PDF/A.
Details	Validating file "x107.pdf" for conformance level pdfa-1b Invalid content of XMP packet header attribute 'begin': '??'. The property 'pdfx:ConTeXt.Support' is not defined in schema 'PDF/X ID Schema'. The property 'pdfx:TeX.Support' is not defined in schema 'PDF/X ID Schema'. The property 'pdfx:LuaTeX.Version' is not defined in schema 'PDF/X ID Schema'. The property 'pdfx:LuaTeX.Functionality' is not defined in schema 'PDF/X ID Schema'. The property 'pdfx:LuaTeX.LuaVersion' is not defined in schema 'PDF/X ID Schema'. The property 'pdfx:LuaTeX.Platform' is not defined in schema 'PDF/X ID Schema'. The document does not conform to the requested standard. The document's meta data is either missing or inconsistent or corrupt. The document does not conform to the PDF/A-1b standard. Done.