Currently, the UI prototype shows the Plus to insert new blocks below the last paragraph (or the paragraph you're writing in). We should consider moving it to the side when you are on a new line. Here's a quick and dirty animatic:

Right after that, start typing and it converts into the type switcher, showing a paragraph block as selected.

This would also tie nicely into the #24, which would then invoke the plus dialog on the left.

This should inform how we can insert content between two blocks. Hover between two blocks to show a blue line and plus on the side:

Or, make a newline and insert, like you would at the end: