Comment 5 for bug 2024343

I've made the schema file validation optional in https://github.com/lxml/lxml/commit/4bfab2c821961fb4c5ed8a04e329778c9b09a1df

This will become available in lxml 5.0. Distributions can now remove only the one file that they dislike and keep the ISO-Schematron support itself intact and available.