should validate attributes by element

[yiminghe]

We mistakenly used required attribute to style label element, such as

<label required>
<label>

label[required] {
  color: red;
}

Soon we found that label's attribute can not be removed in 0.14.x:

ReactDOM.render(<label required>, container);
// update immediately
ReactDOM.render(<label>, container);

After running the above code, The required attribute is still on label element.

Then I realize required is not an attribute of label by standard, just an attribute of some other elements(like input, etc..), so I think required should not be allowed to render at component mount phase like other arbitrary names(such as xyz), else it will cause people confusion.

And I notice that 0.15.x solves this problem by a flag(MUST_USE_PROPERTY), so required is rendered at component mount and will be removed correctly, but is inconsistent with other attributes(select/checked) which is not rendered at all.

So should react validate attributes by element like validateDOMNesting?

[jimfb]

We have a whitelist of attributes, but don't check to ensure they're used on the corresponding tags. With regards to validation, are probably headed in the opposite direction with issues like #140.

However, this may be a reason to set the attribute even if we are already setting the property.

[yiminghe]

I have tested it...

required will be removed by removeAttribute in 0.15.x, but in 0.14.x it will run node.required=undefined to keep required.

[jimfb]

Ah, you are correct. FWIW, we also don't specify the other attributes such as checked/selected in 0.15, unless you are using server side rendering.

[yiminghe]

My mistake, I have edited...

checked/selected are MUST_USE_PROPERTY in 0.15.x, so they are not rendered at all (use node.xx to set)

[jimfb]

I'm going to close this out in favor of #5966, since that's the only actionable part of this issue, as far as I can tell.