In addition to Marcello's post on confusing node names for selection in Dynamo, I'd like to point out what I've just discovered about the Document nodes.
In the API the document that is shown to the user is called Active UIDocument (for brevity uidoc), this element has a property called "Document" that refers to the data base level document (for brevity doc). Any time we want to edit a file in Revit we need to open a transaction that points to a specific doc, while the user interacts with the current uidoc.
In a Revit session there could be multiple docs opened at the same time at a database level (think for instance to a host and links scenario, linked files are documents somehow opened at a database level but not directly editable by the user in the current session; similarly, with multiple editable docs opened, the user is allowed to edit just one at a time, the active document, the uidoc), they could be project or family documents.
The API allows access to those docs without the user interaction and for this reason it's important to have clear in mind the differences between the two: for example, object selections belong to the uidoc (because they require the user intervention), walltypes belong to the doc (because their definition doesn't depend on variables such as the active view), etc.
In the picture above you can see that Document.Current is referring to the UIDocument since I got the active view name, while the Element.Document is referring to the Document since I got the title.
Hope this is gonna be fixed or cleared up in releases to come.
Are you kidding me???