First the facts:
- YourHead plugins don't do any text formatting. All the formatting that is available in YourHead plugins is the same text formatting that you'll find in every RapidWeaver plugin.
- YourHead plugins don't prevent you from using any of the RapidWeaver formatting including inline HTML, the Formatting menu, and the HTML formatting submenu.
The practical implications of these facts are that anything you can place in a Blog or a Styled Text page can be copied and pasted into a Blocks, Stacks, Accordion, or any other plugin without modification. And you should expect the results to look identical, save the obvious differences between Blogs and Accordions.
This also means that all the YourHead plugins are limited to a specific set of styles, just like every other RapidWeaver page. Copying MS Word content into a Styled Text page or a Stacks page will produce similarly awful results. Perhaps one day RapidWeaver will expand its importing capabilities and the YourHead plugins will inherit those improvements, but until then your best bet for importing content is to choose Clear Formatting after importing. Or use Cmd-Opt-V when pasting in content.