[Accessibility] Support AltText for AdaptiveTextBlock

Platform

• .NET WPF
• UWP

(We use the above platforms but this is a schema ask)

Author or host

Author & Host

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1.2.9

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We've been seeing some accessibility issues where the information written in an Adaptive Text Block is not enough information for a narrator user or narrator reads it out strangely. Some examples below

• 1hr is read out as 1 H R (rather than the expected 'One Hour')
• Any text block with a bullet point or unexpected character cannot be read out by narrator so causes accessibility issues.

It would be great if Adaptive could support an altText parameter for Adaptive text blocks (to be read out by screen readers) as part of the schema, that then is used an the screen reader text.

Something like the below

        {
            "type": "TextBlock",
            "text": "1hr",
            "altText": "One hour"
        }

Start by reviewing the Adaptive Cards schema and the accessibility behavior described for .NET WPF and UWP. Determine where a TextBlock altText property would be defined and how screen readers should consume it; the work is done when the schema supports the example and the reported narrator cases have an accessible alternative.