I'm following the plugin tutorial but replacing
editor.insertElement( abbr );
with
editor.insertHtml('<math><msqrt><mn>2</mn></msqrt></math>', 'unfiltered_html');
not work properly once CKEDITOR.filter wasn't disable by the mode option.
NOTE: I had set `allowedContent` to `true` and insert the same HTML in the source editor work properly.
I think that issue is caused
I think that issue is caused by DTD, not the ACF. CKEditor's DTD is defined for HTML5 (although it's not identical, because it's impossible to define DTD for HTML5). You're trying to use MathML, so you'd need to extend the CKEDITOR.dtd object. Unfortunately, I cannot tell if this is going to work perfectly, because we've never tried so huge DTD extension.
Piotrek (Reinmar) Koszuliński
CKEditor JavaScript Developer
--
CKSource - http://cksource.com
--
Follow CKEditor on: Twitter | Facebook | Google+