On 2016-04-13 11:46 AM, Matt King wrote:
> When aria-errormessage was first discussed, my understanding was that the 
> purpose is to distinguish an error message from a description so that 
> assistive technologies would have the option to give it special treatment. 
> Is there more to it than that?

Aria-errormessage is tied to aria-invalid.  The error message is
relevant only when the input is invalid.  In contrast, descriptions have
no specific dependency on validity.

Based on that, the error message is presented only when the input is
invalid.  For a sighted user, the error message is not rendered unless
or until the user has input invalid information.  At that point the
error message is shown near or "attached" to the invalid input.  If the
user corrects the input, the error message vanishes, thereby providing
reinforcement that the error has been corrected.  On the other hand, the
description is presented on demand -- for example, as a tooltip when the
user mouses over the control.  A corollary is that the error message
conveys a sense of urgency or obligation -- something needs to be fixed
-- whereas the description does not.


'Die Wahrheit ist Irgendwo da Drau├čen. Wieder.'
                 - C. Carter -

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