matrix-doc/proposals/1920-stickers-alternative-text.md

Alternative texts for stickers

The current m.sticker event definition includes body as a description field for the sticker. This allows clients to attach a short description of the sticker in an event. So far this field has mainly been used to give a literal description of what is being shown on the image (in the same way an alternative text would do), but the specification says it can also be "a message to accompany and further describe the sticker".

On the one hand it may improve the user experience to use this field for a short text that accompanies the image rather than describing it, on the other hand it's important for accessiblity, and also clients that don't support stickers (or media in general), to have something to use as a down-to-earth description of what's shown in the sticker.

Proposal

Add a new optional alt_text field to the m.sticker event definition which contains the alternative text to the image. A m.sticker event would look like:

{
    "type": "m.sticker",
    "content": {
        "url": "mxc://matrix.org/mRJacbBEPAJczvOltdhABxSv",
        "info": {
            "h": 256,
            "mimetype": "image/png",
            "size": 21957,
            "thumbnail_info": {
                "h": 256,
                "mimetype": "image/png",
                "size": 21957,
                "w": 222
            },
            "thumbnail_url": "mxc://matrix.org/mRJacbBEPAJczvOltdhABxSv",
            "w": 222
        },
        "alt_text": "The white Matrix logo over a black hexagon",
        "body": "Matrix!"
    }
}

In the absence of the alt_text field, clients must use the body as an alternative text.

Tradeoffs

The alt_text field could be a required one, which would be best for accessiblity, but it would break compatibility with the existing m.sticker events.

Conclusion

In general, adding a way to attach an alternative text to every media in Matrix would be a great improvement for accessiblity, but this is out of the scope of this MSC.