When no portal row contains the focus, this function returns 0. If there are multiple windows open in the current
database file, each window can have its own portal row number value, but results are returned for only the foreground window. If a user navigates to a portal without selecting a specific portal row and without making an object active within a specific portal row, Get(ActivePortalRowNumber) returns row 0 rather than row 1.
Returns 5 when the fifth row of a portal has the focus, or when the focus is in a
field in the fifth portal row.
Returns 0 when a portal is not selected.