The "Accessibility" tab in the Info panel checks your site for accessibility issues. Checking a site is a relatively heavy operation so Polypane does not run a check automatically. Start it by clicking the 'Analyse page for accessibility issues'.
You can choose to include best practices or not. While these are not outright failures, they canimpact the accessibility of your site regardless.
Polypane will show a list of issues ordered by severity and highlight any matching WCAG criteria. Click them open to show which elements are affected by an issue and for the issue specific for that element.
When you hover over the element's HTML content, the element will be scrolled to and highlighted in all panes.
Clicking the 'inspect element' editor will show the element in the elements panel so you can quickly debug the issue, then run the accessibility check again (with the reload button in the panel) to check you've solved the issue.
Polypane is filled with accessibility features. We wrote a full overview on our blog: Find and fix accessibility issues with Polypane.
The validators used by the Accessibility panel are the same that power Lighthouse and the web.dev measure score, so a good score in the accessibility panel means a good score in Lighthouse and on web.dev.
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