New in version 2.0.
Get first container element starting before or at prolated_offset:
abjad> staff = Staff("c'8 d'8 e'8 f'8")
abjad> containertools.get_first_element_starting_before_or_at_prolated_offset(staff, Duration(1, 8))
Note("d'8")
Return component.
Return none when no container element starts before or at prolated_offset.
Changed in version 2.0: renamed containertools.get_rightmost_element_starting_not_after_prolated_offset() to containertools.get_first_element_starting_before_or_at_prolated_offset().