Texture Expressions in particular have some extremely un-useful documentation.
The Scene Color node for example: “The SceneColor expression outputs the existing scene color.” That still doesn’t really tell me/us what it does. Also, the description of the node is completely wrong, there is no offset fraction input. The two entries after Scene Colour have no documentation at all.
We’re also still using screenshots from a much earlier version of the Material Editor. I’m all for new features and it’s great that UE is updating so often, but proper concise documentation of what’s currently available really needs to be a higher priority, because a lot of us aren’t getting the most out of the engine.