code: func (d *Decoder) popEOF() bool {
  	if d.stk == nil || d.stk.kind != stkEOF {
  		return false
  	}
  	d.pop()
  	return true
  }
docs: // Undo a pushEOF.
  // The element must have been finished, so the EOF should be at the top of the stack.