Clarify where ngDisabled should be used

[samuraijane]

What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)
Update documentation.

What is the current behavior? (You can also link to an open issue here)
n/a

What is the new behavior (if this is a feature change)?
n/a

Does this PR introduce a breaking change?
No

Please check if the PR fulfills these requirements

• The commit message follows our guidelines: https://github.com/angular/angular.js/blob/master/CONTRIBUTING.md#commit-message-format
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

Other information:

My understanding is that ngDisabled is for form elements only so I propose that the documentation reflect this more clearly.

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[gkalpak]

I think this can be more confusing than helpful. ("form element" often refers to the <form> element.)
How about:

This directive sets the disabled attribute on the element (typically a form control) if the...

[Narretz]

I think there are only these element that natively respond to disabled: option, input, textarea, button, select. Why not list them all?

[gkalpak]

There are more (e.g. optgroup, fieldset). Plus there is nothing stopping people from using it on elements that don't natively respond to disabed, such as custom controls. I wouldn't make too strong a statement (i.e. "it can be used on these elements only). Mentioning the common usecase is fine though (either under the general term "form controls" or by explicit listing).

[Narretz]

Yeah, I meant list all the elements that are supported natively, but not write that they can be used only on these elements. I'm fine with

(typically a form control, e.g. input, button, select etc.)

[samuraijane]

():

[googlebot]

CLAs look good, thanks!

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CLAs look good, thanks!

[Narretz]

@samuraijane No need to close it, you can update the PR.

[samuraijane]

@Narretz Thank you. Still learning how to do this.

[Narretz]

@samuraijane are you going to update this PR? If not, I'm gonna close it, and you can reopen it once you have time to update it.