The visible content portion of Visual Studio is represented by Window
objects, which are instances of open windows within the IDE, such as the Solution Explorer, the Task List window, an open Code Editor window, and so on. Even the IDE itself is represented by a Window
object.
Any given window is either a document window or a tool window. Document windows host documents that are editable by the Text Editor. Tool windows contain controls that display information relevant to the current context of the IDE; the Solution Explorer and Task List windows are examples of tool windows, and a VB source code file open in an editor is an example of a document window.