First macro screen
When macro playback begins, the list of valid next screens is empty (except possibly for transient screens, see Transient screens).
To get candidates for the first macro screen to be processed, the macro runtime searches the entire macro, finds each macro screen that is marked as an entry screen, and adds the names of these macro screens to the list.
The entry screen setting (an attribute of the <screen> element) exists for exactly this purpose, to mark macro screens that can occur as the first screen to be processed.
When a macro is recorded, the Macro object by default marks just the first macro screen to be recorded as an entry screen. After recording is complete, the macro developer can mark (or unmark) any macro screen as an entry screen, and there can be multiple entry screens.
Entry screens are described in more detail in Entry screens.
If no macro screen is marked as an entry screen, then the macro runtime uses all the macro screens in the macro as candidates for the first macro screen to be processed.