Browser hangs and crashes when editing some valid HTML combination

[Rodrigo Siqueira]

On the demo page, edit as "Source" and paste this: <br><ul><pre>TEST</pre></ul>

This will crash the browser when trying to view or edit as html again. Tested in all browsers (Chrome, Firefox, Safari, IE 9).

Seems to be some kind of infinite loop because browser starts using lots of cpu.

[Rodrigo Siqueira]

There are many other valid HTML that also hangs and crashes the editor when editing Source, like this:

<h1>test</h1><br>

<dl>

<dt><h3>test</h3></dt>

</dl>

[Jakub Ś]

To reproduce:

1. Paste one of the below in source and switch to WYSIWYG.

   <h1>test</h1><br /> 
   <dl> 
   <dt><h3>test</h3></dt> 
   </dl> 
   

   <br /><ul><pre>TEST</pre></ul>
   

Result:
Infinite script hanging CKEditor in all browsers from CKEditor 3.6.4 rev [7526]
CKEditor 3.6.4, URI: /ckeditor/_source/core/htmlparser/fragment.js:454
CKEditor 4, URI: ckeditor4/core/htmlparser/fragment.js:417

@rsiqueira Please note that CKEditor 3.x is XHTML1.1 compliant (something like extended HTML4) in which both of these HTML snippets are invalid. You can't have pre directly in ul and dt can hold only inline content.
In CKEditor 4.x which we will try to make fully HTML5 compliant, the example with definition lists is valid. But the key thing here is rather this br tag before the list.

Despite html being valid or not, CKEditor should not hang.

[Jakub Ś]

Other tickets that were caused by this revision are: #9167and #9203.