The WCAG guidelines do a good job of answering questions like these, in my experience. Regarding resizing text, the WCAG guidelines provide the following examp

The WCAG guidelines do a good job of answering questions like these, in my experience. Regarding resizing text, the WCAG guidelines provide the following example of a website that meets the standards: "A user uses a zoom function in his user agent to change the scale of the content. All the content scales uniformly, and the user agent provides scroll bars, if necessary." https://www.w3.org/WAI/WCAG21/Understanding/resize-text.html https://www.w3.org/WAI/WCAG21/Understanding/resize-text.html (There is also a note under the guideline that due to widespread confusion on this specific rule, as long as you meet the basic criteria listed under "sufficient techniques" you are considered OK.) > Does "use an extension for your user-agent to swap out the CSS" count? Yes: https://www.w3.org/WAI/WCAG21/Techniques/general/G156 https://www.w3.org/WAI/WCAG21/Techniques/general/G156 > What is a flash? What is an anything? A flash is "a pair of opposing changes in relative luminance that can cause seizures in some people if it is large enough and in the right frequency range" according to the definitions listed here, along with links to more detailed explanations and examples: https://www.w3.org/WAI/WCAG21/Understanding/three-flashes-or-below-threshold.html#key-terms https://www.w3.org/WAI/WCAG21/Understanding/three-flashes-or... > Can I embed a flashing YouTube video in my user-generated content that I post to make your website in violation of the WCAG? Do you have to implement technical countermeasures to prevent me from doing that? Does YouTube have to prevent users from uploading such content? Clarification on user generated content is part of the WCAG 3.0 working draft, which you can read here: https://www.w3.org/TR/wcag-3.0/#user-generated-content https://www.w3.org/TR/wcag-3.0/#user-generated-content