To validate: The AMP Validator can be used as a web interface at validator.
This interface shows errors displayed inline alongside the HTML source of the page.
It is always recommended to update to the latest release. This repository contains an ANT which allows downloading all necessary tools and artefacts for creating this validator configuration for XRechnung.
If a smart fix is available for an error, then a light bulb icon is shown on the line that generates the error.
When you place the mouse over the icon, a popup appears that lists available smart fixes.
Some editors, including Emacs, can interpret this format and let you jump to the errors in the original file.