code: func (n *ColumnPosition) Accept(v Visitor) (Node, bool) {
  	newNode, skipChildren := v.Enter(n)
  	if skipChildren {
  		return v.Leave(newNode)
  	}
  	n = newNode.(*ColumnPosition)
  	if n.RelativeColumn != nil {
  		node, ok := n.RelativeColumn.Accept(v)
  		if !ok {
  			return n, false
  		}
  		n.RelativeColumn = node.(*ColumnName)
  	}
  	return v.Leave(n)
  }
docs: // Accept implements Node Accept interface.