Content that explains the User Bar & Accessibility Checker

Wagtail 4.2 introduced a new amazing feature, an accessibility checker built in to the Wagtail user bar.

Someone recently asked on Slack about how this feature worked and I searched on the Guide but saw that it is not yet documented there.

I think it would be great to see the user bar generally documented and a call out to the accessibility checker and how to use it.

• https://docs.wagtail.org/en/latest/releases/4.2.html#accessibility-checker-integration
• https://docs.wagtail.org/en/latest/topics/writing_templates.html#wagtailuserbar-tag
• Maybe a new 'Concept' of Page Preview could work https://guide.wagtail.org/en-latest/concepts/ OR a new page under How-to 'view a Preview' - https://guide.wagtail.org/en-latest/how-to-guides/

Start with the linked Wagtail 4.2 accessibility-checker release note and the writing_templates.html section on the wagtailuserbar tag. Review the Guide's Concepts and How-to Guides sections to decide where the User Bar, accessibility checker, and preview guidance belong. Done means the Guide explains how the User Bar and checker work and how editors use them.