index.js
function calcBBox(node, toBBox) {
    distBBox(node, 0, node.children.length, toBBox, node);
}
function calcBBox(node, toBBox) {
    distBBox(node, 0, node.children.length, toBBox, node);
}
function calcBBox ( node , toBBox ) { distBBox ( node , 0 , node . children . length , toBBox , node ) ; }
calculate node's bbox from bboxes of its children
calculate node s bbox from bboxes of its children