fnCheckVisible = function(oNode, oBreaker) {
				if (oNode.nodeState.isLeaf || oNode.nodeState.collapsed
						|| (oNode.nodeState.removed && !oNode.nodeState.reinserted)) {
					bVisible = false;
					oBreaker.broken = true;
				}
			}
Calculates the Length-Delta for the _map algorithm.

@returns {number} The calculated length-delta

@private