code: function handleTagName(schema, tagName, node, stack) {
      // debugger
      var name = typeof tagName === 'string' ? tagName : null
      var ancestors = schema.ancestors
      var length
      var index
  
      if (!name || name === '*' || schema.tagNames.indexOf(name) === -1) {
          return false
      }
  
      ancestors = own.call(ancestors, name) ? ancestors[name] : []
  
      /* Some nodes can break out of their context if they
       * don’t have a certain ancestor. */
      if (ancestors.length !== 0) {
          length = ancestors.length + 1
          index = -1
  
          while (++index < length) {
              if (!ancestors[index]) {
                  return false
              }
  
              if (stack.indexOf(ancestors[index]) !== -1) {
                  break
              }
          }
      }
  
      return name
  }
docs: /* Sanitize `tagName`.