Support 2-level subblock (elements-containers + elements-definitions as children of blocks)

[psyafter]

Nice to have option for subblocks - drug and drop subblock to block

[bwl21]

while playing with another editor which allows sublocks, I find that the newsletter author is likely to be confused by an arbitrary nesting of blocks. OTH the request sounds reasoable. Maybe it makes sense so specify a list of possible parent blocks for a nested block.

[psyafter]

May be not whole subblock but set of possible elements.
For example I want to drugndrop image to text, or some another elements.
Or it can be form element that I want place in another block. And so I want add fields to form...

If it will be supported - so Mosaico can be not just first email template editor but even Landing Pages editor as well

[bago]

I think "free nesting" is not something we'll ever provide, because it is against our "design".
Instead I'd like to support the "subblock", or better, a "block"+"element" layers where a block can declare "elements container".

The only editors I know doing this (campaign monitor editor and beefree) do this with fixed elements. This is also against our current architecture where everything is defined by the template, but I think we can find some good way to implement it.

My main issues are about UX/UI for the "draggable/droppable" elements (development is not easy, but I don't fear it if I have a clear UX+template language idea).