The "Alternative text" box when you edit an image in VE only allows for a single line of text. It should be like the Caption box, which allows for multiple lines of text and automatically expands you enter more text.
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The solution here is fine, but the problem is non-existant. It is a classic case of an solution looking for a problem.
In W3Cs standard (the same organization as was behind HTML4) alternative text is supposed to be short. See https://www.w3.org/TR/2008/NOTE-WCAG20-TECHS-20081211/G94
Also https://en.wikipedia.org/wiki/Wikipedia:Manual_of_Style/Accessibility/Alternative_text_for_images#Basics says the same, so the editor is trying to violate the rules of the project he edits the most to. It so happens that the creator of this ticket pointed out the latter point out to me, so I know he has no valid argument here.
Let's not waste more time than necessary.
@Snaevar I'm reopening this. If after some discussion by all the interested parties it is decided not to implement this feature, that's one thing. I know you disagree with my assessment, and I welcome your input, but I don't think it was appropriate for you to unilaterally close the ticket without discussion.