RFR: JDK-8268335: Find better way to exclude empty HTML elements [v2]

[Jonathan Gibbons]

On Tue, 8 Feb 2022 17:06:03 GMT, Jonathan Gibbons <jjg at openjdk.org> wrote:

> > A few remarks about the rewritten HtmlTree.isEmpty() method: its purpose is to determine whether content is missing in an element that should have content. It therefore always returns false for elements that are expected or allowed to be without content. This is maybe a bit counter-intuitive, but it is what is needed. We could do a combined check such as isVoid() || !isEmpty() but that would still leave out elements that can be empty, such as <script>.
> 
> I agree the current situation is not great, and needs revision, so thanks for taking this on.
> 
> While it may be hard to completely remove the creation and use of empty elements, we should at least try and reduce the number. The current state is a hangover from very-old javadoc, which used print-to-stream before even `HtmlTree`.
> 
> Having `isEmpty` return true for some empty elements is definitely counter-intuitive and suggests the name is wrong. This seems better suited for `isValid` with a definition involving `isVoid` and `isEmpty` as you suggested. I don't quite understanding the comment about `<script>`. Maybe you are wanting a way to mark elements which should not be considered empty, as in "this space intentionally left blank". IIRC, that was the original purpose of `HtmlTree.EMPTY` so perhaps some sort of marker element can stay, perhaps with a better name, to mark HTML elements which should not be marked invalid because they appear to be empty.

Related, maybe `isEmpty`, `isVoid` and `isValid` **all** have a place here, with well-defined semantics.

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PR: https://git.openjdk.java.net/jdk/pull/7159