Illogical Technique

Authors are not going to think about canvas when they want to use a complex image. If they want to use an image they will simply use img.

It is illogical to require img to be encased in canvas in order to provide a long description.

Lacks Long Description Semantics

Semantic elements and attributes improve communication. For details please consult the semantics document.

The semantics of canvas element does not provide a clear, direct, explicit, and strong semantic for an image long description.

Adds Needless Complexity

Requiring canvas to supply long descriptions would introduce needless complexity.

This in turn would make it more prone to authoring error as complexity confuses and leads to errors. longdesc is a simple link - no coordinates to figure out.

Overloads canvas

canvas overloads fallback content.

No Examples in the Wild

No examples in the wild of accessible long text alternatives with canvas have been presented for any of the use cases. No evidence exists that authors have or will use this technique.

Lacks Educational Material

No tutorials, books, or documentation exists that explain to authors how to make an accessible long text alternative with canvas.

No Evidence of Improvement

No evidence has been presented that canvas produces more accessible content for long descriptions than longdesc or that more authors would use it correctly.

Lacks Backwards Compatibility

Any canvas technique for long descriptions lacks backwards compatibility. It is not:

For further rationale please consult the backwards compatibility document.

Retrofitting Problem

Any proposed solution should be easy for authors who are already publishing content with longdesc to retrofit their existing pages. canvas possesses a radically different, authoring pattern than longdesc. Because of this, retrofitting with canvas would be difficult, labor intensive, and error prone.

No retrofitting is required for longdesc as it is an existing HTML feature not a new one.