Hi, I'm adding sibling information to the Block API in the rendering module. There are 3 reasons for this: 1) It'll make a lot of existing method implementations much faster since right now in order to insert or find blocks we have to traverse the list/tree. 2) There's a bug in the current implementation for SpaceBlock since it's immutable and we have a single instance of it. Thus when there are several SpaceBlock in a list doing a list.indexOf(SpaceBlock) will always return the first space block even if you're looking for a subsequent space block. 3) I'm implementing a generic emoticon Transformation and I need to get the sibling of a block. Just shout if you think there's a better way of doing it. I'm implementing it now. Thanks -Vincent