How to enrich Neos.NodeTypes:Title

Using Neos & Flow Frontend & Integration
1

Our Designer has a new hobby. All headers get subheaders. And for him the perfect way to do this is like this:

<h1>
    Title
    <br>
    <span>Subtitle</span>
</h1>

or

<h2>
    <span>Subtitle</span>
    <br>
    Title
</h1>

Generally I’m fine with that idea. So I added https://github.com/techdivision/ckstyles. Now I’m able to mark the part that should be the subheader. This works fine as well.

But now I need the help of the community in the next step:
When I get back to this page in backend, it loads the page and shows the correct structure. But one second later, when the inline editing is loaded, it pushes the span out of the header and the code ends up like this:

<h1>
    Title
</h1>
<span>
    <span>Subtitle</span>
</span>

Is there anything I can do against this?

2

One more thing. I activated the formating option strong and put the styles for the subheader at that element. So now there is:

<h1>
    Title
    <br/>
    <strong>Subtitle</strong>
</h1>

This is a somehow workarround.

So it seems like there is a possibility to specify which tags are allowed inside of the editing field and which of them will be pushed out of the tag.