As the name of this function indicates, this arrowhead design is borrowed from MetaPost, although there are differences. The main idea with the design is that the arrowhead should bend with the path, please refer to the canonical illustration on the MetaPost home page. The argument ahLength suggests how long the arrowhead should be (this will only be overridden in exceptional cases when the path is too short). If it is not provided, its value will be computed based on the width of the stroke and ahAngle — exactly how will remain subject to change for some time. ahAngle is the angle at the tip of the arrowhead. When fillAsStroking is true, the fill color of the arrowhead will be ..Shapes..Traits..@stroking instead of ..Shapes..Traits..@nonstroking.