nl_tokens: TODO Allow control point to be customized .
pl_tokens: function chord ( d , i ) { var s = subgroup ( this , source , d , i ) , t = subgroup ( this , <mask> , d , i ) ; return "M" + s . p0 + arc ( s . r , s . p1 ) + ( equals ( s , t ) ? curve ( s . r , s . p1 , s . r , s . p0 ) : curve ( s . r , s . p1 , t . r , t . p0 ) + arc ( t . r , t . p1 ) + curve ( t . r , t . p1 , s . r , s . p0 ) ) + "Z" ; }