Default marker of the series that is displayed as a bubble. It is nil by default.

Flag determining if the bubbles should be automatically laid out to prevent their intersections (YES) or they should be positioned in their exact coordinates given by the data source (NO). The default value is NO. If YES, an iterative quasi-physical gas simulation algorithm is applied, where bubbles repulse by Archimedean force and attract to their given positions by Hooke’s law.