Terms

The following terms are used in this reference:

Main form Delphi form where you place TApXXXDialog component. It does not mean that it's the main form of your application of course.
Left, Top, Right, Bottom forms These terms refer to Delphi forms wich are used in your application as left, top, right and bottom parts of your custom dialog.
Custom form This term refers to form wich can be used in your dialog in any way. Now this term refers to replacement of shell list view control in open/save dialogs (CustDlgParams.CutomForm property) and of shell tree view in folder dialog.
Additional dialog forms Refers to all these forms (except Main)

The following picture shows you Main form:

mainform.jpg (16671 bytes)

And this picture illustrates additional dialog forms:

addforms.jpg (30172 bytes)