They've used `required={true}`, not `required="true"`, which is JSX, not HTML. The one with curlies isn't even valid HTML. In the old HTML spec, the correct value, if you wanted to set a value, was to set `required="required"`, but these days the spec is looser since it tries to conform to the web, not the other way around.
Even in jsx its not required to add a boolean value. Unless you are passing in a var as a prop in which case sure. But that didn't look like it was the case in these examples.
> Even in jsx its not required to add a boolean value
Absolutely true! But I like to do it because I personally think it reads more nicely and is more explicit and that's what I do in all my projects. But it is indeed a matter of taste and I have nothing against code that follows the convention to omit the "true" value.