blocksVisibility method
Returns true if this node represents root of was imported by reference
Implementation
bool blocksVisibility() {
visibilityBlocks ??= 0;
return visibilityBlocks != 0;
//2.5.3 20151120
// Node.prototype.blocksVisibility = function () {
// if (this.visibilityBlocks == null) {
// this.visibilityBlocks = 0;
// }
// return this.visibilityBlocks !== 0;
// };
}