iframe should not self-close.
Adding class to an element that already had a class would fail
Merge branch 'pr/20' into development
Three community bug fixes (huge thanks!)

- Eric Desbiens (olace): Adding class to an element that already had a
class would fail
- Zegnat: iframes should not self-close
- Peter: Typo
with `$this::XML` should be `$this->XML`