You can add comments to document render trees. For example, you can describe what they are supposed to do and how they work.
You can add a comment for an individual node by right-clicking over it (not over a port) and choosing Create Comment.
You can add a Comment node from the Comment category. Comment nodes are not attached to a specific node
You can add a Group Comment node from the Comment category to document a block of nodes. Group comments are especially useful because you can middle-click on the label to select and move the entire group (the comment and all other nodes that are contained or overlap). In addition, their background color shows up in the Bird's Eye View, making it easy to locate specific areas of a tree.
Comments work the same way in the render tree as they do in the ICE tree. For complete details, see Documenting Trees: Groups and Comments [ICE Fundamentals].