[Intro page] Design patterns to avoid

[rianrietveld]

URL: https://wpaccessibility.org/docs/topics/design/avoid/
Code: https://github.com/wpaccessibility/wp-a11y-docs/blob/main/docs/topics/design/avoid/index.md

Please read How to contribute before you start.

Tasks

The intro text needs to be written.