Transition MVC TagHelpers to use TargetElementAttributes attribute targeting.

[NTaylorMullen]

Now that TagHelpers can target attributes we should transition our existing TagHelpers to utilize this new "required" attributes functionality.

One example: ValidationSummaryTagHelper shouldn't target "div" elements then no-op if the attribute doesn't exist: It should target the asp-validation-summary attribute on any HTML element.

This should also enable us to no longer have ambiguity between "should I be a tag helper" for all of our tag helpers.

[dougbu]

it's likely views would perform better if tag helpers were not created only to no-op. however we should measure things to confirm this is worthwhile since the MVC tag helpers are doing simple checks that work today.

specifically:

ValidationSummaryTagHelper shouldn't target "div" elements then no-op if the attribute doesn't exist: It should target the asp-validation-summary attribute on any HTML element.

"any" is too broad. we likely want to target <div> and <span> and that's about it. in any case, we should strive to preserve the chosen behaviour and limit work on this issue to the implementation choice. deal with reevaluating the behaviours separately.

This should also enable us to no longer have ambiguity between "should I be a tag helper" ...

could you clarify this statement? is this another point about changing the current MVC tag helper behaviours?

[danroth27]

@DamianEdwards Let us know if you think we need to pull this back into the current milestone.

[DamianEdwards]

We should do this now

[NTaylorMullen]

@dougbu The ambiguity bit I mentioned will drastically improve TagHelper tooling. For instance, today in the pre-bits for TagHelper tooling every div tag is highlighted because of the validation summary maybe being a TagHelper on div elements. Same thing goes for all other TagHelpers.

[dougbu]

@NTaylorMullen thanks, that was much clearer

[ajaybhargavb]

Part 1 - bfdeda7
Part 2 - e205890
Part 3 - fd5e07d