The original inventor of a popular XML standard, Rick Jelliffe, who created Schematron, has protested that the widely used text is now behind a paywall at standards body ISO.
Schematron is a language for validating XML, designed for processing XML documents and reporting on errors. Version 1.0 was developed in 1999, since when it has been enhanced and standardised, with the latest version being ISO/IEC 19757-3:2020.
The Schematron standard is one of those administered by a JTC (Joint Technical Committee), called ISO/IEC JTC 1/SC 34, which oversees "Document description and processing languages."
In the case of the 2020 edition, which is some corrections and additional annexes only to the freely available 2016 edition, it is ridiculous bastardry on ISO's part
This also includes both the Microsoft-sponsored Office Open XML and the OpenDocument format used by LibreOffice and Apache OpenOffice, in liaison with other standards groups including Ecma International and OASIS.