Sheets in macOS are a way of displaying a modal dialog over a window. A sheet is document modal — it prevents the user from using the window (or other windows in a window hierarchy) until the sheet is dismissed.
VAqua supports displaying any Java window as a sheet (the window does not have to be a Dialog). The Java window must have an owner window; the sheet is attached to the owner window. The sheet is dismissed when its Java window is hidden or disposed. It is up to the application to hide or dispose the Java window. Typically, the window is hidden or disposed by an event listener associated with a button in the window, such as an accept or cancel button.
The current Swing architecture does not enable a look and feel to transparently implement sheets. Moreover, the current Java API for document modal dialogs is seriously flawed. Therefore, VAqua supports sheets using a new API called VSheet, which is part of the VAquaClient library.