Select whole block of code till end and delete using delete key. It changes the type of next block. I am not sure if this is bug or intended behavior.
Technically, you’re deleting from the start of the heading to the start of the paragraph, and the code would leave the heading opening token intact and wrap the paragraph’s text in it. I agree this isn’t great, and
replaceRange already adjusts the deleted range in other situations, so I’ve added code to cover this case and make it delete the entire start block, leaving the text as a paragraph.
The change has been released as prosemirror-transform 1.0.7