Handle <style> tag

[maxbarnas]

Suggested merge commit message (convention)

Other (engine): The <style> tag will not interfere with the editing experience. Closes #11104.

Feature (html-support): Added <style> tag support. Closes #11104.

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Additional information

For example – encountered issues, assumptions you had to make, other affected tickets, etc.

[Reinmar]

"While rendering the editor content, the ..."

"To avoid this, the <style> element was replaced with ..."

[maxbarnas]

Fixed.

[Reinmar]

Isn't it a leftover from the <script>'s tests?

[maxbarnas]

Fixed.

[Reinmar]

I improved the manual tests a bit because there was no place where I could easily test the change.

Issue 1.

I stumbled upon an odd issue (probably not a blocker for this PR).

The below content works fine:

<p>
    x
</p>
<script>a</script><style>a</style>
<p>
    x
</p>

However, this gets miss-formatted after being passed via setData->getData:

<p>
    x
</p>
<script>a</script>
<style>a</style>
<p>
    x
</p>

Upon setData() this becomes:

<p>x</p><script>a</script><p>&nbsp;<style>a</style></p><p>x</p>

For some reason, the new line character is not correctly ignored by DomConverter and probably then we have a chain reaction of incorrect autoparagraphing.

Issue 2.

This issue is not a blocker as well, but should be resolved soon.

Try this:

editor.setData( '<script>a</script>');
editor.getData();

An empty string is returned. Same for a lone <style>. This is probably an excessive "empty content trimming".

[maxbarnas]

Second issue is definitely a separate topic that exists for a long time. The first one though... that's new. Should I create a ticket for that?

[Reinmar]

Both deserve tickets. Could you search whether they exist already and if not open new ones? 

I'd also like to prioritize the second one because it may lead to data loss.

[Reinmar]

I commented under the second error, but it makes sense to update both. I'll do that.

[maxbarnas]

I commented under the second error, but it makes sense to update both. I'll do that.

Ah! I thought it was specifically directed at the <style> error. Especially since the old one seemed fine before. Thanks for the fix.

[Reinmar]

Both had the same issue – they missed the context of what's happening. Something was detected... but when? Integrators have no idea what DomConverter is. They might even start worrying that their script tags were completely lost. My changes make the former clearer and slightly (although, not completely) help with the latter. So the error could be made even better, explaining that this is happening only inside the editor.

[maxbarnas]

Here are those two tickets for the problems found on review: #11247 and #11248.