The label sub location is a fallback for when an invalid case is encountered
by the primary location. When the primary location is 'top' or 'bottom'
and the line is perfectly vertical, then the sub location would be used.
Similarly, if the primary location is 'left' or 'right' and the line is
perfectly horizontal, then the sub location would be used.
Label sub location relative to line.
'top' | 'left' | 'bottom' | 'right'The label sub location is a fallback for when an invalid case is encountered by the primary location. When the primary location is
'top'or'bottom'and the line is perfectly vertical, then the sub location would be used.Similarly, if the primary location is
'left'or'right'and the line is perfectly horizontal, then the sub location would be used.