POSIX::mblen() Make thread-safe; allow shift state control

[perl5.git] / utf8.h

diff --git a/utf8.h b/utf8.h
index dd4d1e1..fb83507 100644 (file)
--- a/utf8.h
+++ b/utf8.h
@@ -144,11 +144,6 @@ EXTCONST unsigned char PL_utf8skip[];
 
 END_EXTERN_C
 
 
 END_EXTERN_C
 

-#if defined(_MSC_VER) && _MSC_VER < 1400
-/* older MSVC versions have a smallish macro buffer */
-#define PERL_SMALL_MACRO_BUFFER
-#endif
-

 /*
 
 =for apidoc Am|U8|NATIVE_TO_LATIN1|U8 ch
 /*
 
 =for apidoc Am|U8|NATIVE_TO_LATIN1|U8 ch


@@ -194,13 +189,8 @@ adding no time nor space requirements to the implementation.
 =cut
 */
 
 =cut
 */
 

-#ifdef PERL_SMALL_MACRO_BUFFER
-#  define NATIVE_TO_LATIN1(ch)     ((U8)(ch))
-#  define LATIN1_TO_NATIVE(ch)     ((U8)(ch))
-#else
-#  define NATIVE_TO_LATIN1(ch)     (__ASSERT_(FITS_IN_8_BITS(ch)) ((U8) ((ch) | 0)))
-#  define LATIN1_TO_NATIVE(ch)     (__ASSERT_(FITS_IN_8_BITS(ch)) ((U8) ((ch) | 0)))
-#endif
+#define NATIVE_TO_LATIN1(ch)     (__ASSERT_(FITS_IN_8_BITS(ch)) ((U8) ((ch) | 0)))
+#define LATIN1_TO_NATIVE(ch)     (__ASSERT_(FITS_IN_8_BITS(ch)) ((U8) ((ch) | 0)))

 
 /* I8 is an intermediate version of UTF-8 used only in UTF-EBCDIC.  We thus
  * consider it to be identical to UTF-8 on ASCII platforms.  Strictly speaking
 
 /* I8 is an intermediate version of UTF-8 used only in UTF-EBCDIC.  We thus
  * consider it to be identical to UTF-8 on ASCII platforms.  Strictly speaking


@@ -208,13 +198,8 @@ adding no time nor space requirements to the implementation.
  * because they are 8-bit encodings that serve the same purpose in Perl, and
  * rarely do we need to distinguish them.  The term "NATIVE_UTF8" applies to
  * whichever one is applicable on the current platform */
  * because they are 8-bit encodings that serve the same purpose in Perl, and
  * rarely do we need to distinguish them.  The term "NATIVE_UTF8" applies to
  * whichever one is applicable on the current platform */

-#ifdef PERL_SMALL_MACRO_BUFFER
-#define NATIVE_UTF8_TO_I8(ch) ((U8) (ch))
-#define I8_TO_NATIVE_UTF8(ch) ((U8) (ch))
-#else

 #define NATIVE_UTF8_TO_I8(ch) (__ASSERT_(FITS_IN_8_BITS(ch)) ((U8) ((ch) | 0)))
 #define I8_TO_NATIVE_UTF8(ch) (__ASSERT_(FITS_IN_8_BITS(ch)) ((U8) ((ch) | 0)))
 #define NATIVE_UTF8_TO_I8(ch) (__ASSERT_(FITS_IN_8_BITS(ch)) ((U8) ((ch) | 0)))
 #define I8_TO_NATIVE_UTF8(ch) (__ASSERT_(FITS_IN_8_BITS(ch)) ((U8) ((ch) | 0)))

-#endif

 
 #define UNI_TO_NATIVE(ch)        ((UV) ((ch) | 0))
 #define NATIVE_TO_UNI(ch)        ((UV) ((ch) | 0))
 
 #define UNI_TO_NATIVE(ch)        ((UV) ((ch) | 0))
 #define NATIVE_TO_UNI(ch)        ((UV) ((ch) | 0))


@@ -272,60 +257,7 @@ Perl's extended UTF-8 means we can have start bytes up through FF, though any
 beginning with FF yields a code point that is too large for 32-bit ASCII
 platforms.  FF signals to use 13 bytes for the encoded character.  This breaks
 the paradigm that the number of leading bits gives how many total bytes there
 beginning with FF yields a code point that is too large for 32-bit ASCII
 platforms.  FF signals to use 13 bytes for the encoded character.  This breaks
 the paradigm that the number of leading bits gives how many total bytes there

-are in the character.
-
-=cut
-*/
-
-/* Is the representation of the Unicode code point 'cp' the same regardless of
- * being encoded in UTF-8 or not? */
-#define OFFUNI_IS_INVARIANT(cp)     isASCII(cp)
-
-/*
-=for apidoc Am|bool|UVCHR_IS_INVARIANT|UV cp
-
-Evaluates to 1 if the representation of code point C<cp> is the same whether or
-not it is encoded in UTF-8; otherwise evaluates to 0.  UTF-8 invariant
-characters can be copied as-is when converting to/from UTF-8, saving time.
-C<cp> is Unicode if above 255; otherwise is platform-native.
-
-=cut
- */
-
-#define UVCHR_IS_INVARIANT(cp)      OFFUNI_IS_INVARIANT(cp)
-
-/* Misleadingly named: is the UTF8-encoded byte 'c' part of a variant sequence
- * in UTF-8?  This is the inverse of UTF8_IS_INVARIANT.  The |0 makes sure this
- * isn't mistakenly called with a ptr argument */
-#define UTF8_IS_CONTINUED(c)  (__ASSERT_(FITS_IN_8_BITS(c))                 \
-                               ((U8)((c) | 0)) &  UTF_CONTINUATION_MARK)
-
-/* Is the byte 'c' the first byte of a multi-byte UTF8-8 encoded sequence?
- * This doesn't catch invariants (they are single-byte).  It also excludes the
- * illegal overlong sequences that begin with C0 and C1.  The |0 makes sure
- * this isn't mistakenly called with a ptr argument */
-#define UTF8_IS_START(c)      (__ASSERT_(FITS_IN_8_BITS(c))                 \
-                               ((U8)((c) | 0)) >= 0xc2)
-
-/* Is the byte 'c' part of a multi-byte UTF8-8 encoded sequence, and not the
- * first byte thereof?  The |0 makes sure this isn't mistakenly called with a
- * ptr argument */
-#define UTF8_IS_CONTINUATION(c)     (__ASSERT_(FITS_IN_8_BITS(c))           \
-     (((U8)((c) | 0)) & UTF_IS_CONTINUATION_MASK) == UTF_CONTINUATION_MARK)
-
-/* Is the UTF8-encoded byte 'c' the first byte of a two byte sequence?  Use
- * UTF8_IS_NEXT_CHAR_DOWNGRADEABLE() instead if the input isn't known to
- * be well-formed.  Masking with 0xfe allows the low bit to be 0 or 1; thus
- * this matches 0xc[23].  The |0 makes sure this isn't mistakenly called with a
- * ptr argument */
-#define UTF8_IS_DOWNGRADEABLE_START(c) (__ASSERT_(FITS_IN_8_BITS(c))       \
-                                         (((U8)((c) | 0)) & 0xfe) == 0xc2)
-
-/* Is the UTF8-encoded byte 'c' the first byte of a sequence of bytes that
- * represent a code point > 255?  The |0 makes sure this isn't mistakenly
- * called with a ptr argument */
-#define UTF8_IS_ABOVE_LATIN1(c)     (__ASSERT_(FITS_IN_8_BITS(c))           \
-                                     ((U8)((c) | 0)) >= 0xc4)
+are in the character. */

 
 /* This is the number of low-order bits a continuation byte in a UTF-8 encoded
  * sequence contributes to the specification of the code point.  In the bit
 
 /* This is the number of low-order bits a continuation byte in a UTF-8 encoded
  * sequence contributes to the specification of the code point.  In the bit


@@ -363,6 +295,29 @@ C<cp> is Unicode if above 255; otherwise is platform-native.
  * the underlying reason that B0 works here) */
 #define UTF_CONTINUATION_MARK       (UTF_IS_CONTINUATION_MASK & 0xB0)
 
  * the underlying reason that B0 works here) */
 #define UTF_CONTINUATION_MARK       (UTF_IS_CONTINUATION_MASK & 0xB0)
 

+/* Is the byte 'c' part of a multi-byte UTF8-8 encoded sequence, and not the
+ * first byte thereof? */
+#define UTF8_IS_CONTINUATION(c)     (__ASSERT_(FITS_IN_8_BITS(c))           \
+            (((NATIVE_UTF8_TO_I8(c) & UTF_IS_CONTINUATION_MASK)             \
+                                                == UTF_CONTINUATION_MARK)))
+
+/* Is the representation of the Unicode code point 'cp' the same regardless of
+ * being encoded in UTF-8 or not? This is a fundamental property of
+ * UTF-8,EBCDIC */
+#define OFFUNI_IS_INVARIANT(c) (((WIDEST_UTYPE)(c)) < UTF_CONTINUATION_MARK)
+
+/*
+=for apidoc Am|bool|UVCHR_IS_INVARIANT|UV cp
+
+Evaluates to 1 if the representation of code point C<cp> is the same whether or
+not it is encoded in UTF-8; otherwise evaluates to 0.  UTF-8 invariant
+characters can be copied as-is when converting to/from UTF-8, saving time.
+C<cp> is Unicode if above 255; otherwise is platform-native.
+
+=cut
+ */
+#define UVCHR_IS_INVARIANT(cp)  (OFFUNI_IS_INVARIANT(NATIVE_TO_UNI(cp)))
+

 /* Internal macro to be used only in this file to aid in constructing other
  * publicly accessible macros.
  * The number of bytes required to express this uv in UTF-8, for just those
 /* Internal macro to be used only in this file to aid in constructing other
  * publicly accessible macros.
  * The number of bytes required to express this uv in UTF-8, for just those


@@ -421,6 +376,39 @@ encoded as UTF-8.  C<cp> is a native (ASCII or EBCDIC) code point if less than
  */
 #define UVCHR_SKIP(uv) ( UVCHR_IS_INVARIANT(uv) ? 1 : __BASE_UNI_SKIP(uv))
 
  */
 #define UVCHR_SKIP(uv) ( UVCHR_IS_INVARIANT(uv) ? 1 : __BASE_UNI_SKIP(uv))
 

+#define UTF_MIN_START_BYTE                                                  \
+     ((UTF_CONTINUATION_MARK >> UTF_ACCUMULATION_SHIFT) | UTF_START_MARK(2))
+
+/* Is the byte 'c' the first byte of a multi-byte UTF8-8 encoded sequence?
+ * This excludes invariants (they are single-byte).  It also excludes the
+ * illegal overlong sequences that begin with C0 and C1 on ASCII platforms, and
+ * C0-C4 I8 start bytes on EBCDIC ones.  On EBCDIC E0 can't start a
+ * non-overlong sequence, so we define a base macro and for those platforms,
+ * extend it to also exclude E0 */
+#define UTF8_IS_START_base(c)    (__ASSERT_(FITS_IN_8_BITS(c))              \
+                             (NATIVE_UTF8_TO_I8(c) >= UTF_MIN_START_BYTE))
+#ifdef EBCDIC
+#  define UTF8_IS_START(c)                                                  \
+                (UTF8_IS_START_base(c) && (c) != I8_TO_NATIVE_UTF8(0xE0))
+#else
+#  define UTF8_IS_START(c)  UTF8_IS_START_base(c)
+#endif
+
+#define UTF_MIN_ABOVE_LATIN1_BYTE                                           \
+                    ((0x100 >> UTF_ACCUMULATION_SHIFT) | UTF_START_MARK(2))
+
+/* Is the UTF8-encoded byte 'c' the first byte of a sequence of bytes that
+ * represent a code point > 255? */
+#define UTF8_IS_ABOVE_LATIN1(c)     (__ASSERT_(FITS_IN_8_BITS(c))           \
+                        (NATIVE_UTF8_TO_I8(c) >= UTF_MIN_ABOVE_LATIN1_BYTE))
+
+/* Is the UTF8-encoded byte 'c' the first byte of a two byte sequence?  Use
+ * UTF8_IS_NEXT_CHAR_DOWNGRADEABLE() instead if the input isn't known to
+ * be well-formed. */
+#define UTF8_IS_DOWNGRADEABLE_START(c) (__ASSERT_(FITS_IN_8_BITS(c))       \
+                inRANGE(NATIVE_UTF8_TO_I8(c),                               \
+                        UTF_MIN_START_BYTE, UTF_MIN_ABOVE_LATIN1_BYTE - 1))
+

 /* The largest code point representable by two UTF-8 bytes on this platform.
  * As explained in the comments for __COMMON_UNI_SKIP, 32 start bytes with
  * UTF_ACCUMULATION_SHIFT bits of information each */
 /* The largest code point representable by two UTF-8 bytes on this platform.
  * As explained in the comments for __COMMON_UNI_SKIP, 32 start bytes with
  * UTF_ACCUMULATION_SHIFT bits of information each */


@@ -431,18 +419,26 @@ encoded as UTF-8.  C<cp> is a native (ASCII or EBCDIC) code point if less than
  * continuation byte */
 #define MAX_PORTABLE_UTF8_TWO_BYTE (32 * (1U << 5) - 1)
 
  * continuation byte */
 #define MAX_PORTABLE_UTF8_TWO_BYTE (32 * (1U << 5) - 1)
 

-/* The maximum number of UTF-8 bytes a single Unicode character can
- * uppercase/lowercase/fold into.  Unicode guarantees that the maximum
- * expansion is UTF8_MAX_FOLD_CHAR_EXPAND characters, but any above-Unicode
- * code point will fold to itself, so we only have to look at the expansion of
- * the maximum Unicode code point.  But this number may be less than the space
- * occupied by a very large code point under Perl's extended UTF-8.  We have to
- * make it large enough to fit any single character.  (It turns out that ASCII
- * and EBCDIC differ in which is larger) */
+/*
+
+=for apidoc AmnU|STRLEN|UTF8_MAXBYTES_CASE
+
+The maximum number of UTF-8 bytes a single Unicode character can
+uppercase/lowercase/titlecase/fold into.
+
+=cut
+
+ * Unicode guarantees that the maximum expansion is UTF8_MAX_FOLD_CHAR_EXPAND
+ * characters, but any above-Unicode code point will fold to itself, so we only
+ * have to look at the expansion of the maximum Unicode code point.  But this
+ * number may be less than the space occupied by a very large code point under
+ * Perl's extended UTF-8.  We have to make it large enough to fit any single
+ * character.  (It turns out that ASCII and EBCDIC differ in which is larger)
+ *
+=cut
+*/

 #define UTF8_MAXBYTES_CASE                                                     \
 #define UTF8_MAXBYTES_CASE                                                     \

-        (UTF8_MAXBYTES >= (UTF8_MAX_FOLD_CHAR_EXPAND * OFFUNISKIP(0x10FFFF))    \
-                           ? UTF8_MAXBYTES                                      \
-                           : (UTF8_MAX_FOLD_CHAR_EXPAND * OFFUNISKIP(0x10FFFF)))
+            MAX(UTF8_MAXBYTES, UTF8_MAX_FOLD_CHAR_EXPAND * OFFUNISKIP(0x10FFFF))

 
 /* Rest of these are attributes of Unicode and perl's internals rather than the
  * encoding, or happen to be the same in both ASCII and EBCDIC (at least at
 
 /* Rest of these are attributes of Unicode and perl's internals rather than the
  * encoding, or happen to be the same in both ASCII and EBCDIC (at least at


@@ -465,7 +461,7 @@ encoded as UTF-8.  C<cp> is a native (ASCII or EBCDIC) code point if less than
  * UTF-8 encoded character that mark it as a start byte and give the number of
  * bytes that comprise the character. 'len' is the number of bytes in the
  * multi-byte sequence. */
  * UTF-8 encoded character that mark it as a start byte and give the number of
  * bytes that comprise the character. 'len' is the number of bytes in the
  * multi-byte sequence. */

-#define UTF_START_MARK(len) (((len) >  7) ? 0xFF : (0xFF & (0xFE << (7-(len)))))
+#define UTF_START_MARK(len) (((len) >  7) ? 0xFF : ((U8) (0xFE << (7-(len)))))

 
 /* Masks out the initial one bits in a start byte, leaving the real data ones.
  * Doesn't work on an invariant byte.  'len' is the number of bytes in the
 
 /* Masks out the initial one bits in a start byte, leaving the real data ones.
  * Doesn't work on an invariant byte.  'len' is the number of bytes in the


@@ -535,15 +531,62 @@ encoded as UTF-8.  C<cp> is a native (ASCII or EBCDIC) code point if less than
 /*
 
 =for apidoc Am|STRLEN|UTF8SKIP|char* s
 /*
 
 =for apidoc Am|STRLEN|UTF8SKIP|char* s

-returns the number of bytes in the UTF-8 encoded character whose first (perhaps
-only) byte is pointed to by C<s>.
+returns the number of bytes a non-malformed UTF-8 encoded character whose first
+(perhaps only) byte is pointed to by C<s>.
+
+If there is a possibility of malformed input, use instead:
+
+=over
+
+=item L</C<UTF8_SAFE_SKIP>> if you know the maximum ending pointer in the
+buffer pointed to by C<s>; or
+
+=item L</C<UTF8_CHK_SKIP>> if you don't know it.
+
+=back
+
+It is better to restructure your code so the end pointer is passed down so that
+you know what it actually is at the point of this call, but if that isn't
+possible, L</C<UTF8_CHK_SKIP>> can minimize the chance of accessing beyond the end
+of the input buffer.

 
 =cut
  */
 #define UTF8SKIP(s)  PL_utf8skip[*(const U8*)(s)]
 
 =cut
  */
 #define UTF8SKIP(s)  PL_utf8skip[*(const U8*)(s)]

+
+/*
+=for apidoc Am|STRLEN|UTF8_SKIP|char* s
+This is a synonym for L</C<UTF8SKIP>>
+
+=cut
+*/
+

 #define UTF8_SKIP(s) UTF8SKIP(s)
 
 /*
 #define UTF8_SKIP(s) UTF8SKIP(s)
 
 /*

+=for apidoc Am|STRLEN|UTF8_CHK_SKIP|char* s
+
+This is a safer version of L</C<UTF8SKIP>>, but still not as safe as
+L</C<UTF8_SAFE_SKIP>>.  This version doesn't blindly assume that the input
+string pointed to by C<s> is well-formed, but verifies that there isn't a NUL
+terminating character before the expected end of the next character in C<s>.
+The length C<UTF8_CHK_SKIP> returns stops just before any such NUL.
+
+Perl tends to add NULs, as an insurance policy, after the end of strings in
+SV's, so it is likely that using this macro will prevent inadvertent reading
+beyond the end of the input buffer, even if it is malformed UTF-8.
+
+This macro is intended to be used by XS modules where the inputs could be
+malformed, and it isn't feasible to restructure to use the safer
+L</C<UTF8_SAFE_SKIP>>, for example when interfacing with a C library.
+
+=cut
+*/
+
+#define UTF8_CHK_SKIP(s)                                                       \
+            (s[0] == '\0' ? 1 : MIN(UTF8SKIP(s),                               \
+                                    my_strnlen((char *) (s), UTF8SKIP(s))))
+/*

 
 =for apidoc Am|STRLEN|UTF8_SAFE_SKIP|char* s|char* e
 returns 0 if S<C<s E<gt>= e>>; otherwise returns the number of bytes in the
 
 =for apidoc Am|STRLEN|UTF8_SAFE_SKIP|char* s|char* e
 returns 0 if S<C<s E<gt>= e>>; otherwise returns the number of bytes in the


@@ -588,6 +631,11 @@ with a ptr argument.
  * above show, doesn't matter as to its implementation */
 #define NATIVE_BYTE_IS_INVARIANT(c)    UVCHR_IS_INVARIANT(c)
 
  * above show, doesn't matter as to its implementation */
 #define NATIVE_BYTE_IS_INVARIANT(c)    UVCHR_IS_INVARIANT(c)
 

+/* Misleadingly named: is the UTF8-encoded byte 'c' part of a variant sequence
+ * in UTF-8?  This is the inverse of UTF8_IS_INVARIANT. */
+#define UTF8_IS_CONTINUED(c)  (__ASSERT_(FITS_IN_8_BITS(c))                 \
+                               (! UTF8_IS_INVARIANT(c)))
+

 /* The macros in the next 4 sets are used to generate the two utf8 or utfebcdic
  * bytes from an ordinal that is known to fit into exactly two (not one) bytes;
  * it must be less than 0x3FF to work across both encodings. */
 /* The macros in the next 4 sets are used to generate the two utf8 or utfebcdic
  * bytes from an ordinal that is known to fit into exactly two (not one) bytes;
  * it must be less than 0x3FF to work across both encodings. */


@@ -644,30 +692,15 @@ with a ptr argument.
  * beginning of a utf8 character.  Now that foo_utf8() determines that itself,
  * no need to do it again here
  */
  * beginning of a utf8 character.  Now that foo_utf8() determines that itself,
  * no need to do it again here
  */

-#define isIDFIRST_lazy_if(p,UTF)                                            \
-            _is_utf8_FOO(_CC_IDFIRST, (const U8 *) p, "isIDFIRST_lazy_if",  \
-                         "isIDFIRST_lazy_if_safe",                          \
-                         cBOOL(UTF && ! IN_BYTES), 0, __FILE__,__LINE__)
-

 #define isIDFIRST_lazy_if_safe(p, e, UTF)                                   \
                    ((IN_BYTES || !UTF)                                      \
                      ? isIDFIRST(*(p))                                      \
                      : isIDFIRST_utf8_safe(p, e))
 #define isIDFIRST_lazy_if_safe(p, e, UTF)                                   \
                    ((IN_BYTES || !UTF)                                      \
                      ? isIDFIRST(*(p))                                      \
                      : isIDFIRST_utf8_safe(p, e))

-
-#define isWORDCHAR_lazy_if(p,UTF)                                           \
-            _is_utf8_FOO(_CC_IDFIRST, (const U8 *) p, "isWORDCHAR_lazy_if", \
-                         "isWORDCHAR_lazy_if_safe",                         \
-                         cBOOL(UTF && ! IN_BYTES), 0, __FILE__,__LINE__)
-

 #define isWORDCHAR_lazy_if_safe(p, e, UTF)                                  \
                    ((IN_BYTES || !UTF)                                      \
                      ? isWORDCHAR(*(p))                                     \
                      : isWORDCHAR_utf8_safe((U8 *) p, (U8 *) e))
 #define isWORDCHAR_lazy_if_safe(p, e, UTF)                                  \
                    ((IN_BYTES || !UTF)                                      \
                      ? isWORDCHAR(*(p))                                     \
                      : isWORDCHAR_utf8_safe((U8 *) p, (U8 *) e))

-
-#define isALNUM_lazy_if(p,UTF)                                              \
-            _is_utf8_FOO(_CC_IDFIRST, (const U8 *) p, "isALNUM_lazy_if",    \
-                         "isWORDCHAR_lazy_if_safe",                         \
-                         cBOOL(UTF && ! IN_BYTES), 0, __FILE__,__LINE__)
+#define isALNUM_lazy_if_safe(p, e, UTF) isWORDCHAR_lazy_if_safe(p, e, UTF)

 
 #define UTF8_MAXLEN UTF8_MAXBYTES
 
 
 #define UTF8_MAXLEN UTF8_MAXBYTES
 


@@ -898,6 +931,10 @@ Evaluates to 0xFFFD, the code point of the Unicode REPLACEMENT CHARACTER
 #define UNICODE_DISALLOW_NONCHAR       0x0020
 #define UNICODE_DISALLOW_SUPER         0x0040
 #define UNICODE_DISALLOW_PERL_EXTENDED 0x0080
 #define UNICODE_DISALLOW_NONCHAR       0x0020
 #define UNICODE_DISALLOW_SUPER         0x0040
 #define UNICODE_DISALLOW_PERL_EXTENDED 0x0080

+
+#ifdef PERL_CORE
+#  define UNICODE_ALLOW_ABOVE_IV_MAX   0x0100
+#endif

 #define UNICODE_DISALLOW_ABOVE_31_BIT  UNICODE_DISALLOW_PERL_EXTENDED
 
 #define UNICODE_GOT_SURROGATE       UNICODE_DISALLOW_SURROGATE
 #define UNICODE_DISALLOW_ABOVE_31_BIT  UNICODE_DISALLOW_PERL_EXTENDED
 
 #define UNICODE_GOT_SURROGATE       UNICODE_DISALLOW_SURROGATE


@@ -972,7 +1009,13 @@ Evaluates to 0xFFFD, the code point of the Unicode REPLACEMENT CHARACTER
 
 #define UNI_DISPLAY_ISPRINT    0x0001
 #define UNI_DISPLAY_BACKSLASH  0x0002
 
 #define UNI_DISPLAY_ISPRINT    0x0001
 #define UNI_DISPLAY_BACKSLASH  0x0002

-#define UNI_DISPLAY_QQ         (UNI_DISPLAY_ISPRINT|UNI_DISPLAY_BACKSLASH)
+#define UNI_DISPLAY_BACKSPACE  0x0004  /* Allow \b when also
+                                           UNI_DISPLAY_BACKSLASH */
+#define UNI_DISPLAY_QQ         (UNI_DISPLAY_ISPRINT                \
+                                |UNI_DISPLAY_BACKSLASH              \
+                                |UNI_DISPLAY_BACKSPACE)
+
+/* Character classes could also allow \b, but not patterns in general */

 #define UNI_DISPLAY_REGEX      (UNI_DISPLAY_ISPRINT|UNI_DISPLAY_BACKSLASH)
 
 #define ANYOF_FOLD_SHARP_S(node, input, end)   \
 #define UNI_DISPLAY_REGEX      (UNI_DISPLAY_ISPRINT|UNI_DISPLAY_BACKSLASH)
 
 #define ANYOF_FOLD_SHARP_S(node, input, end)   \