In the current editor using nested <sub></sub> html is supported, and can achieve an extra small fontsize. For example: <sub><sub> Extra Small </sub></sub>
When writing this in the Markdown version of the RT editor, and then switching over to RT the first <sub> gets trimmed, the last </sub> doesn't: <sub>Extra Small</sub> </sub>
Either nested <sub> statements should be supported, or the last closing argument should also be trimmed.