You specify a frame as pop‑up by setting IsPopup to TRUE in the optionlist when you invoke the frame's Property Inspector.

User-specified pop‑up frames can be invoked to display on top of active and inactive parent frames. To access an active parent frame that has been covered by a child pop‑up, the user must move it adjacent to the pop‑up. The parent can never overlay the pop‑up, which prevents the pop‑up from being hidden by the parent. You can specify the usual frame attributes for a pop‑up frame, such as resizability.

Pop‑up frames must be called by a parent frame or procedure. Starting frames cannot be pop‑ups. If a pop‑up is specified as the starting frame for an application, it is treated as a standard frame at runtime, as is a pop‑up frame run from the Go menu of the Frame Editor.

If a pop‑up frame is invoked by an object that is not itself viewable, such as a procedure or ghost frame, it displays in relation to the closest viewable ancestor (for example, the frame that called the procedure).