Potential accessibility issues to fix

[mialondon]

From https://web.dev/measure/ for https://www.libcrowds.com/collection/playbills

• High Accessibility [role] values are not valid
• High Accessibility Buttons do not have an accessible name
• High Accessibility Image elements do not have [alt] attributes
• Low Accessibility Heading elements are not in a sequentially-descending order
• Low Accessibility Links do not have a discernible name
• Low Accessibility Lists do not contain only <li> elements and script supporting elements (<script> and <template>).

For https://www.libcrowds.com/collection/playbills/projects

• High Accessibility [role] values are not valid
• High Accessibility Image elements do not have [alt] attributes
• Low Accessibility Heading elements are not in a sequentially-descending order
• Low Accessibility Links do not have a discernible name
• Low Accessibility Lists do not contain only <li> elements and script supporting elements (<script> and <template>).

For an example task page https://www.libcrowds.com/collection/playbills/projects/260/iiif-annotation

• High Accessibility [role] values are not valid
• Low Accessibility Lists do not contain only <li> elements and script supporting elements (<script> and <template>).

From https://web.dev/measure/ for https://www.libcrowds.com/ - will apply to all LibCrowds projects

• High Performance Properly size images
• High Performance Defer offscreen images
• High Performance Remove unused JavaScript
• High Performance Serve images in next-gen formats
• High Performance Reduce initial server response time
• High Accessibility Image elements do not have [alt] attributes
• Medium Performance Avoid serving legacy JavaScript to modern browsers
• Medium Best Practices Does not use HTTPS [actually the site says it is https?]
• Medium Best Practices Links to cross-origin destinations are unsafe
• Medium Best Practices Includes front-end JavaScript libraries with known security vulnerabilities
• Medium Best Practices Missing source maps for large first-party JavaScript
• Medium SEO Links do not have descriptive text
• Medium SEO Image elements do not have [alt] attributes
• Low Accessibility Heading elements are not in a sequentially-descending order
• Low Accessibility Links do not have a discernible name
• Low Accessibility Lists do not contain only <li> elements and script supporting elements (<script> and <template>).

[mialondon]

Looking at the front page, 'Crowdsourcing projects from the British Library' needs to be H1.

Is https://www.digitalocean.com/community/tutorials/vuejs-vuejs-accessible-announcements vue-announcer a useful option?

[mialondon]

Notes for outsourced developer with context on the site's purpose and identified issues for core and task pages: https://docs.google.com/document/d/1NzZfeof4dl0PhqksHYxougZ4OCGu-vwwJUJWwqiRpIs/edit?usp=sharing

[mialondon]

Updates after UAT at #884