code: function canHasNodeAsChild(tag, node) {
          // document can nest any tag
          if (tag.nodeType === 9) {
              return 1;
          }
          if (!dtd[tag.tagName]) {
              throw new Error('dtd[' + tag.tagName + '] === undefined!');
          }
          if (node.nodeType === 8) {
              return 1;
          }
          var nodeName = node.tagName || node.nodeName;
          return !!dtd[tag.tagName][nodeName];
      }
docs: /*
  checked whether tag can include node as its child according to DTD
   /*
  checked whether tag can include node as its child according to DTD