Moving to a ‘Block-based’ editing system was first outlined in the ‘How Little Blocks Work‘ announcement post in May 2017. This was an opportunity to look at a brand new way to store content data in WordPress:
The new block-based development logic was outlined by Matias Ventura as:
Blocks provide functions that describe how they want to be represented for both the editing context and the final markup to be saved. The internal representation of the post content is updated as blocks are updated, so during the editing session we can remain in the right side of the diagram above.
Further information can be found in the ‘Editor Technical Overview‘ which is where the idea of using ‘HTML comments’ as a way to separate block content started out.