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+* ABOUT BUGS
+
+Before reporting a bug, please check the list of known bugs
+and the list of oft-reported non-bugs (below).
+
+Bugs and comments may be sent to bonzini@gnu.org; please
+include in the Subject: header the first line of the output of
+"sed --version".
+
+Please do not send a bug report like this:
+
+        [while building frobme-1.3.4]
+        $ configure
+        sed: file sedscr line 1: Unknown option to 's'
+
+If sed doesn't configure your favorite package, take a few extra
+minutes to identify the specific problem and make a stand-alone test
+case.
+
+A stand-alone test case includes all the data necessary to perform the
+test, and the specific invocation of sed that causes the problem.  The
+smaller a stand-alone test case is, the better.  A test case should
+not involve something as far removed from sed as "try to configure
+frobme-1.3.4".  Yes, that is in principle enough information to look
+for the bug, but that is not a very practical prospect.
+
+
+
+* NON-BUGS
+
+'N' command on the last line
+
+  Most versions of sed exit without printing anything when the 'N'
+  command is issued on the last line of a file.  GNU sed instead
+  prints pattern space before exiting unless of course the '-n'
+  command switch has been specified.  More information on the reason
+  behind this choice can be found in the Info manual.
+
+
+regex syntax clashes (problems with backslashes)
+
+  sed uses the Posix basic regular expression syntax.  According to
+  the standard, the meaning of some escape sequences is undefined in
+  this syntax;  notable in the case of GNU sed are '\|', '\+', '\?',
+  '\'', '\'', '\<', '\>', '\b', '\B', '\w', and '\W'.
+
+  As in all GNU programs that use Posix basic regular expressions, sed
+  interprets these escape sequences as meta-characters.  So, 'x\+'
+  matches one or more occurrences of 'x'.   'abc\|def' matches either
+  'abc' or 'def'.
+
+  This syntax may cause problems when running scripts written for other
+  seds.  Some sed programs have been written with the assumption that
+  '\|' and '\+' match the literal characters '|' and '+'.  Such scripts
+  must be modified by removing the spurious backslashes if they are to
+  be used with recent versions of sed (not only GNU sed).
+
+  On the other hand, some scripts use 's|abc\|def||g' to remove occurrences
+  of _either_ 'abc' or 'def'.  While this worked until sed 4.0.x, newer
+  versions interpret this as removing the string 'abc|def'.  This is
+  again undefined behavior according to POSIX, but this interpretation
+  is arguably more robust: the older one, for example, required that
+  the regex matcher parsed '\/' as '/' in the common case of escaping
+  a slash, which is again undefined behavior; the new behavior avoids
+  this, and this is good because the regex matcher is only partially
+  under our control.
+
+  In addition, GNU sed supports several escape characters (some of
+  which are multi-character) to insert non-printable characters
+  in scripts ('\a', '\c', '\d', '\o', '\r', '\t', '\v', '\x').  These
+  can cause similar problems with scripts written for other seds.
+
+
+-i clobbers read-only files
+
+  In short, 'sed d -i' will let one delete the contents of
+  a read-only file, and in general the '-i' option will let
+  one clobber protected files.  This is not a bug, but rather a
+  consequence of how the Unix file system works.
+
+  The permissions on a file say what can happen to the data
+  in that file, while the permissions on a directory say what can
+  happen to the list of files in that directory.  'sed -i'
+  will not ever open for writing  a file that is already on disk,
+  rather, it will work on a temporary file that is finally renamed
+  to the original name: if you rename or delete files, you're actually
+  modifying the contents of the directory, so the operation depends on
+  the permissions of the directory, not of the file).  For this same
+  reason, sed will not let one use '-i' on a writeable file in a
+  read-only directory, and will break hard or symbolic links when
+  '-i' is used on such a file.
+
+
+'0a' does not work (gives an error)
+
+  There is no line 0.  0 is a special address that is only used to treat
+  addresses like '0,/RE/' as active when the script starts: if you
+  write '1,/abc/d' and the first line includes the word 'abc', then
+  that match would be ignored because address ranges must span at least
+  two lines (barring the end of the file); but what you probably wanted is
+  to delete every line up to the first one including 'abc', and this
+  is obtained with '0,/abc/d'.
+
+
+'[a-z]' is case insensitive
+'s/.*//' does not clear pattern space
+
+  You are encountering problems with locales.  POSIX mandates that '[a-z]'
+  uses the current locale's collation order -- in C parlance, that means
+  strcoll(3) instead of strcmp(3).  Some locales have a case insensitive
+  strcoll, others don't.
+
+  Another problem is that [a-z] tries to use collation symbols.  This
+  only happens if you are on the GNU system, using GNU libc's regular
+  expression matcher instead of compiling the one supplied with GNU sed.
+  In a Danish locale, for example, the regular expression '^[a-z]$'
+  matches the string 'aa', because 'aa' is a single collating symbol that
+  comes after 'a' and before 'b'; 'll' behaves similarly in Spanish
+  locales, or 'ij' in Dutch locales.
+
+  Another common localization-related problem happens if your input stream
+  includes invalid multibyte sequences.  POSIX mandates that such
+  sequences are _not_ matched by '.', so that 's/.*//' will not clear
+  pattern space as you would expect.  In fact, there is no way to clear
+  sed's buffers in the middle of the script in most multibyte locales
+  (including UTF-8 locales).  For this reason, GNU sed provides a 'z'
+  command (for 'zap') as an extension.
+
+  However, to work around both of these problems, which may cause bugs
+  in shell scripts, you can set the LC_ALL environment variable to 'C',
+  or set the locale on a more fine-grained basis with the other LC_*
+  environment variables.