Describe the new a11y feature or project enhancement

This is not an a11y mistake by itself, but it is something that I've seen in most accessibility checkers: showing a warning when there's a link to a Word, Excel, PowerPoint, or PDF document. Also, when there's a link to Youtube (because captioning is often missing or not well generated).

Those documents often have accessibility issues and need to be created with accessibility in mind. Also, they may be loaded on the browser, but they require plugins/extensions that can create navigation difficulties.

Describe the solution you'd like

Show a warning about potential accessibility issues when:

• A link to a PDF, Word, Excel, or PowerPoint document is present on the page.
• A link to Youtube is present on the document.

This can be done in CSS by checking the end of the URL looking for certain extensions (".pdf", ".doc", ".docx", ".xls", etc.), or the beginning of the URL looking for Youtube addresses ("https://youtu.be", "https://youtube.com", etc.)

Link(s)

• WebAIM Wave Guidelines (will link to Google Docs) <-- this list may be interesting to add more CSS-only features to Checka11y.css.