"AL":  arm.C_SCOND_NONE,
	"U":   arm.C_UBIT,
	"S":   arm.C_SBIT,
	"W":   arm.C_WBIT,
	"P":   arm.C_PBIT,
	"PW":  arm.C_WBIT | arm.C_PBIT,
	"WP":  arm.C_WBIT | arm.C_PBIT,
	"F":   arm.C_FBIT,
	"IBW": arm.C_WBIT | arm.C_PBIT | arm.C_UBIT,
	"IAW": arm.C_WBIT | arm.C_UBIT,
	"DBW": arm.C_WBIT | arm.C_PBIT,
	"DAW": arm.C_WBIT,
	"IB":  arm.C_PBIT | arm.C_UBIT,
	"IA":  arm.C_UBIT,
	"DB":  arm.C_PBIT,
	"DA":  0,
}

// Copyright 2013 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// The linkcheck command finds missing links in the godoc website.
// It crawls a URL recursively and notes URLs and URL fragments
// that it's seen and prints a report of missing links at the end.
package main

import (
	"errors"
	"flag"
	"fmt"
	"io"
	"log"
	"net/http"
	"os"

---
title: "Go, Backwards Compatibility, and GODEBUG"
layout: article
---

<!--
This document is kept in the Go repo, not x/website,
because it documents the full list of known GODEBUG settings,
which are tied to a specific release.
-->

## Introduction {#intro}

Go's emphasis on backwards compatibility is one of its key strengths.
There are, however, times when we cannot maintain complete compatibility.