Studyo now supports the notion of optional sections. From Insights, an administrator can define a section as optional per occurrence or per semester, with a maximum time window where students can enroll in an occurrence or a series of occurrences, and a maximum number of students who can enroll.
When an optional period is available to a student, they see a small green triangle in the corner.
They can select that triangle to see the list of available section occurrences and pick one.
Once selected, the optional class will appear normally in the period.
As the teacher of such a section, you can manage your class' roster by opening any period (selecting the period's colored band in "Day", "Week" or "Teacher" view).
You can use that list to help you take attendance and can make changes if a student shows up at the last minute, for example.