code: func CopyToken(t Token) Token {
  	switch v := t.(type) {
  	case CharData:
  		return v.Copy()
  	case Comment:
  		return v.Copy()
  	case Directive:
  		return v.Copy()
  	case ProcInst:
  		return v.Copy()
  	case StartElement:
  		return v.Copy()
  	}
  	return t
  }
docs: // CopyToken returns a copy of a Token.