[xwiki-devs] [Proposal] Rendering refactoring: introduce the notion of original blocks to the core Block API

Hi devs, This is a bit technical but after brainstorming with Thomas we came to the conclusion that in order to implement "generic marker" support the best solution would be to add the notion of original blocks to the Block interface itself. This will results in 2 things: * adding new begin/endOriginalBlocks events (in Listener.java) * adding a CollectionBlock that is a non content block used simply to group together one or several blocks. We'll need it in the following use case: when a single block is replaced with several blocks, we'll need to wrap the several blocks in a CollectionBlock that has an originalBlocks field set to the previous single block. It's also needed in some other use cases, for example when a block is replaced by a leaf block (non father block), we need a wrapper block to group together begin/endOriginal blocks and the new block events. In summary the idea is to not require a new generic marker block and instead set the notion of original block in the Block interface itself. WDYT? Thanks -Vincent