The Authoring Tool Accessibility Guidelines (ATAG) 2.0 provides guidelines for designing web content authoring tools that are both more accessible to authors with disabilities (Part A) and designed to enable, support, and promote the production of more accessible web content by all authors (Part B).
For Wagtail, as an authoring tool, ATAG is the most relevant standard to follow.
ATAG 2.0, available in multiple formats:
We manually create an audit report in Markdown, then transpose the results in the ATAG Report Tool. Finally, we report findings in the WAI Authoring Tools List.