O que é chamado quando uma janela está dentro de outra janela e restrita à janela do host?
Esse será um exemplo de Windows MDI (Multiple Document Interface):
Frame, Client, and Child Windows
An MDI application has three kinds of windows: a frame window, an MDI client window, as well as a number of child windows. The frame window is like the main window of the application: it has a sizing border, a title bar, a window menu, a minimize button, and a maximize button. The application must register a window class for the frame window and provide a window procedure to support it.
An MDI application does not display output in the client area of the frame window. Instead, it displays the MDI client window. An MDI client window is a special type of child window belonging to the preregistered window class MDICLIENT. The client window is a child of the frame window; it serves as the background for child windows. It also provides support for creating and manipulating child windows. For example, an MDI application can create, activate, or maximize child windows by sending messages to the MDI client window.
When the user opens or creates a document, the client window creates a child window for the document. The client window is the parent window of all MDI child windows in the application. Each child window has a sizing border, a title bar, a window menu, a minimize button, and a maximize button. Because a child window is clipped, it is confined to the client window and cannot appear outside it.
An MDI application can support more than one kind of document. For example, a typical spreadsheet application enables the user to work with both charts and spreadsheets. For each type of document that it supports, an MDI application must register a child window class and provide a window procedure to support the windows belonging to that class. For more information about window classes, see Window Classes. For more information about window procedures, see Window Procedures.
Following is a typical MDI application. It is named Multipad.
Fonte Sobre a interface de vários documentos
Eu quero desenvolver um programa Visual Basic com esta função.
Dê uma olhada nas Aplicativos de Interface de Documentos Múltiplos (MDI) :
Creating an MDI Application
Use the following procedure to create an MDI form and its child forms.
To create an MDI application
Create an MDI form.
From the Project menu, choose Add MDI Form.
Note An application can have only one MDI form. If a project already has an MDI form, the Add MDI Form command on the Project menu is unavailable.
Create the application's child forms.
To create an MDI child form, create a new form (or open an existing one) and set its MDIChild property to True.
Veja também Formulário MDI , que contém um guia para criando um VB 6.0 MDI Editor.