code: function augment(left, right) {
      var data
      var ctx
  
      // Handle `data.hName`, `data.hProperties, `hChildren`.
      if (left && 'data' in left) {
        data = left.data
  
        if (right.type === 'element' && data.hName) {
          right.tagName = data.hName
        }
  
        if (right.type === 'element' && data.hProperties) {
          right.properties = xtend(right.properties, data.hProperties)
        }
  
        if (right.children && data.hChildren) {
          right.children = data.hChildren
        }
      }
  
      ctx = left && left.position ? left : {position: left}
  
      if (!generated(ctx)) {
        right.position = {
          start: position.start(ctx),
          end: position.end(ctx)
        }
      }
  
      return right
    }
docs: Finalise the created `right`, a hast node, from `left`, an mdast node.