diff --git a/example/json-to-cbor/json-to-cbor.cc b/example/json-to-cbor/json-to-cbor.cc
index d8d7a3d..7d2bdfe 100644
--- a/example/json-to-cbor/json-to-cbor.cc
+++ b/example/json-to-cbor/json-to-cbor.cc
@@ -275,6 +275,11 @@
                       : Append(static_cast<uint64_t>(-(val + 1)), 0x20);
   }
 
+  virtual std::string AppendByteString(std::string&& val) {
+    TRY(Append(val.size(), 0x40));
+    return write_dst(val.data(), val.size());
+  }
+
   virtual std::string AppendTextString(std::string&& val) {
     TRY(Append(val.size(), 0x60));
     return write_dst(val.data(), val.size());
diff --git a/internal/cgen/auxiliary/cbor.cc b/internal/cgen/auxiliary/cbor.cc
index 976bf9b..b736bb6 100644
--- a/internal/cgen/auxiliary/cbor.cc
+++ b/internal/cgen/auxiliary/cbor.cc
@@ -27,9 +27,10 @@
     : error_message(std::move(error_message0)),
       cursor_position(cursor_position0) {}
 
-void DecodeCborCallbacks::Done(DecodeCborResult& result,
-                               sync_io::Input& input,
-                               IOBuffer& buffer) {}
+void  //
+DecodeCborCallbacks::Done(DecodeCborResult& result,
+                          sync_io::Input& input,
+                          IOBuffer& buffer) {}
 
 DecodeCborResult  //
 DecodeCbor(DecodeCborCallbacks&& callbacks,
diff --git a/internal/cgen/auxiliary/cbor.hh b/internal/cgen/auxiliary/cbor.hh
index a16b49a..75853a3 100644
--- a/internal/cgen/auxiliary/cbor.hh
+++ b/internal/cgen/auxiliary/cbor.hh
@@ -62,6 +62,8 @@
   //
   // Do not keep a reference to buffer or buffer.data.ptr after Done returns,
   // as DecodeCbor may then de-allocate the backing array.
+  //
+  // The default Done implementation is a no-op.
   virtual void Done(DecodeCborResult& result,
                     sync_io::Input& input,
                     IOBuffer& buffer);
diff --git a/internal/cgen/auxiliary/json.cc b/internal/cgen/auxiliary/json.cc
index e40b308..7b8556d 100644
--- a/internal/cgen/auxiliary/json.cc
+++ b/internal/cgen/auxiliary/json.cc
@@ -27,9 +27,15 @@
     : error_message(std::move(error_message0)),
       cursor_position(cursor_position0) {}
 
-void DecodeJsonCallbacks::Done(DecodeJsonResult& result,
-                               sync_io::Input& input,
-                               IOBuffer& buffer) {}
+std::string  //
+DecodeJsonCallbacks::AppendByteString(std::string&& val) {
+  return "wuffs_aux::JsonDecoder: unexpected JSON byte string";
+}
+
+void  //
+DecodeJsonCallbacks::Done(DecodeJsonResult& result,
+                          sync_io::Input& input,
+                          IOBuffer& buffer) {}
 
 DecodeJsonResult  //
 DecodeJson(DecodeJsonCallbacks&& callbacks,
@@ -158,13 +164,43 @@
             const char* ptr =  // Convert from (uint8_t*).
                 static_cast<const char*>(static_cast<void*>(token_ptr));
             str.append(ptr, token_len);
+          } else if (
+              vbd &
+              WUFFS_BASE__TOKEN__VBD__STRING__CONVERT_1_DST_4_SRC_BACKSLASH_X) {
+            wuffs_base__slice_u8 encoded =
+                wuffs_base__make_slice_u8(token_ptr, token_len);
+            while (encoded.len > 0) {
+              uint8_t decoded[64];
+              constexpr bool src_closed = true;
+              wuffs_base__transform__output o = wuffs_base__base_16__decode4(
+                  wuffs_base__make_slice_u8(&decoded[0], sizeof decoded),
+                  encoded, src_closed, WUFFS_BASE__BASE_16__DEFAULT_OPTIONS);
+              if (o.status.is_error()) {
+                ret_error_message = o.status.message();
+                goto done;
+              } else if ((o.num_dst > (sizeof decoded)) ||
+                         (o.num_src > encoded.len)) {
+                ret_error_message =
+                    "wuffs_aux::JsonDecoder: internal error: inconsistent "
+                    "base16 decoding";
+                goto done;
+              }
+              str.append(  // Convert from (uint8_t*).
+                  static_cast<const char*>(static_cast<void*>(&decoded[0])),
+                  o.num_dst);
+              encoded.ptr += o.num_src;
+              encoded.len -= o.num_src;
+            }
           } else {
             goto fail;
           }
           if (token.continued()) {
             continue;
           }
-          ret_error_message = callbacks.AppendTextString(std::move(str));
+          ret_error_message =
+              (vbd & WUFFS_BASE__TOKEN__VBD__STRING__CHAIN_MUST_BE_UTF_8)
+                  ? callbacks.AppendTextString(std::move(str))
+                  : callbacks.AppendByteString(std::move(str));
           str.clear();
           goto parsed_a_value;
         }
diff --git a/internal/cgen/auxiliary/json.hh b/internal/cgen/auxiliary/json.hh
index b3998f6..a310f93 100644
--- a/internal/cgen/auxiliary/json.hh
+++ b/internal/cgen/auxiliary/json.hh
@@ -31,10 +31,21 @@
   // strings, the Callbacks implementation is responsible for tracking map keys
   // versus other values.
 
+  // The JSON file format as specified deals only with (UTF-8) text strings,
+  // but an unofficial extension allows "ijk\x89m" escapes within those
+  // strings. DecodeJsonCallbacks' AppendByteString will not be called unless
+  // WUFFS_JSON__QUIRK_ALLOW_BACKSLASH_X_AS_BYTES is passed to DecodeJson. If
+  // it is passed, AppendTextString will not be called and all byte strings are
+  // potentially invalid UTF-8. It is up to the AppendByteString implementation
+  // whether to test the std::string for UTF-8 validity.
+  //
+  // The default AppendByteString implementation returns an error message.
+
   virtual std::string AppendNull() = 0;
   virtual std::string AppendBool(bool val) = 0;
   virtual std::string AppendF64(double val) = 0;
   virtual std::string AppendI64(int64_t val) = 0;
+  virtual std::string AppendByteString(std::string&& val);
   virtual std::string AppendTextString(std::string&& val) = 0;
 
   // Push and Pop are called for container nodes: JSON arrays (lists) and JSON
@@ -60,6 +71,8 @@
   //
   // Do not keep a reference to buffer or buffer.data.ptr after Done returns,
   // as DecodeJson may then de-allocate the backing array.
+  //
+  // The default Done implementation is a no-op.
   virtual void Done(DecodeJsonResult& result,
                     sync_io::Input& input,
                     IOBuffer& buffer);
diff --git a/internal/cgen/data/data.go b/internal/cgen/data/data.go
index 140349f..a96060c 100644
--- a/internal/cgen/data/data.go
+++ b/internal/cgen/data/data.go
@@ -626,43 +626,45 @@
 	""
 
 const AuxCborCc = "" +
-	"// ---------------- Auxiliary - CBOR\n\n#if !defined(WUFFS_CONFIG__MODULES) || defined(WUFFS_CONFIG__MODULE__AUX__CBOR)\n\n#include <utility>\n\nnamespace wuffs_aux {\n\nDecodeCborResult::DecodeCborResult(std::string&& error_message0,\n                                   uint64_t cursor_position0)\n    : error_message(std::move(error_message0)),\n      cursor_position(cursor_position0) {}\n\nvoid DecodeCborCallbacks::Done(DecodeCborResult& result,\n                               sync_io::Input& input,\n                               IOBuffer& buffer) {}\n\nDecodeCborResult  //\nDecodeCbor(DecodeCborCallbacks&& callbacks,\n           sync_io::Input&& input,\n           wuffs_base__slice_u32 quirks) {\n  // Prepare the wuffs_base__io_buffer and the resultant error_message.\n  wuffs_base__io_buffer* io_buf = input.BringsItsOwnIOBuffer();\n  wuffs_base__io_buffer fallback_io_buf = wuffs_base__empty_io_buffer();\n  std::unique_ptr<uint8_t[]> fallback_io_array(nullptr);\n  if (!io_buf) {\n    fallback_io_array = std::unique_ptr<uint8_t[]>(ne" +
-	"w uint8_t[4096]);\n    fallback_io_buf = wuffs_base__ptr_u8__writer(fallback_io_array.get(), 4096);\n    io_buf = &fallback_io_buf;\n  }\n  size_t cursor_index = 0;\n  std::string ret_error_message;\n  std::string io_error_message;\n\n  do {\n    // Prepare the low-level CBOR decoder.\n    wuffs_cbor__decoder::unique_ptr dec = wuffs_cbor__decoder::alloc();\n    if (!dec) {\n      ret_error_message = \"wuffs_aux::CborDecoder: out of memory\";\n      goto done;\n    }\n    for (size_t i = 0; i < quirks.len; i++) {\n      dec->set_quirk_enabled(quirks.ptr[i], true);\n    }\n\n    // Prepare the wuffs_base__tok_buffer.\n    wuffs_base__token tok_array[256];\n    wuffs_base__token_buffer tok_buf =\n        wuffs_base__slice_token__writer(wuffs_base__make_slice_token(\n            &tok_array[0], (sizeof(tok_array) / sizeof(tok_array[0]))));\n    wuffs_base__status tok_status = wuffs_base__make_status(nullptr);\n\n    // Prepare other state.\n    uint32_t depth = 0;\n    std::string str;\n    int64_t extension_category = 0;\n    uint64_t extension" +
-	"_detail = 0;\n\n    // Valid token's VBCs range in 0 ..= 15. Values over that are for tokens\n    // from outside of the base package, such as the CBOR package.\n    constexpr int64_t EXT_CAT__CBOR_TAG = 16;\n\n    // Loop, doing these two things:\n    //  1. Get the next token.\n    //  2. Process that token.\n    while (true) {\n      // 1. Get the next token.\n\n      while (tok_buf.meta.ri >= tok_buf.meta.wi) {\n        if (tok_status.repr == nullptr) {\n          // No-op.\n        } else if (tok_status.repr == wuffs_base__suspension__short_write) {\n          tok_buf.compact();\n        } else if (tok_status.repr == wuffs_base__suspension__short_read) {\n          // Read from input to io_buf.\n          if (!io_error_message.empty()) {\n            ret_error_message = std::move(io_error_message);\n            goto done;\n          } else if (cursor_index != io_buf->meta.ri) {\n            ret_error_message =\n                \"wuffs_aux::CborDecoder: internal error: bad cursor_index\";\n            goto done;\n          } else if" +
-	" (io_buf->meta.closed) {\n            ret_error_message =\n                \"wuffs_aux::CborDecoder: internal error: io_buf is closed\";\n            goto done;\n          }\n          io_buf->compact();\n          if (io_buf->meta.wi >= io_buf->data.len) {\n            ret_error_message =\n                \"wuffs_aux::CborDecoder: internal error: io_buf is full\";\n            goto done;\n          }\n          cursor_index = io_buf->meta.ri;\n          io_error_message = input.CopyIn(io_buf);\n        } else {\n          ret_error_message = tok_status.message();\n          goto done;\n        }\n\n        if (WUFFS_CBOR__DECODER_WORKBUF_LEN_MAX_INCL_WORST_CASE != 0) {\n          ret_error_message =\n              \"wuffs_aux::CborDecoder: internal error: bad WORKBUF_LEN\";\n          goto done;\n        }\n        wuffs_base__slice_u8 work_buf = wuffs_base__empty_slice_u8();\n        tok_status = dec->decode_tokens(&tok_buf, io_buf, work_buf);\n      }\n\n      wuffs_base__token token = tok_buf.data.ptr[tok_buf.meta.ri++];\n      uint64_t t" +
-	"oken_len = token.length();\n      if ((io_buf->meta.ri < cursor_index) ||\n          ((io_buf->meta.ri - cursor_index) < token_len)) {\n        ret_error_message =\n            \"wuffs_aux::CborDecoder: internal error: bad token indexes\";\n        goto done;\n      }\n      uint8_t* token_ptr = io_buf->data.ptr + cursor_index;\n      cursor_index += token_len;\n\n      // 2. Process that token.\n\n      uint64_t vbd = token.value_base_detail();\n\n      if (extension_category != 0) {\n        int64_t ext = token.value_extension();\n        if ((ext >= 0) && !token.continued()) {\n          extension_detail = (extension_detail\n                              << WUFFS_BASE__TOKEN__VALUE_EXTENSION__NUM_BITS) |\n                             static_cast<uint64_t>(ext);\n          switch (extension_category) {\n            case WUFFS_BASE__TOKEN__VBC__INLINE_INTEGER_SIGNED:\n              extension_category = 0;\n              ret_error_message =\n                  callbacks.AppendI64(static_cast<int64_t>(extension_detail));\n              g" +
-	"oto parsed_a_value;\n            case WUFFS_BASE__TOKEN__VBC__INLINE_INTEGER_UNSIGNED:\n              extension_category = 0;\n              ret_error_message = callbacks.AppendU64(extension_detail);\n              goto parsed_a_value;\n            case EXT_CAT__CBOR_TAG:\n              extension_category = 0;\n              ret_error_message = callbacks.AppendCborTag(extension_detail);\n              if (!ret_error_message.empty()) {\n                goto done;\n              }\n              continue;\n          }\n        }\n        ret_error_message =\n            \"wuffs_aux::CborDecoder: internal error: bad extended token\";\n        goto done;\n      }\n\n      switch (token.value_base_category()) {\n        case WUFFS_BASE__TOKEN__VBC__FILLER:\n          continue;\n\n        case WUFFS_BASE__TOKEN__VBC__STRUCTURE: {\n          if (vbd & WUFFS_BASE__TOKEN__VBD__STRUCTURE__PUSH) {\n            ret_error_message = callbacks.Push(static_cast<uint32_t>(vbd));\n            if (!ret_error_message.empty()) {\n              goto done;\n   " +
-	"         }\n            depth++;\n            continue;\n          }\n          ret_error_message = callbacks.Pop(static_cast<uint32_t>(vbd));\n          depth--;\n          goto parsed_a_value;\n        }\n\n        case WUFFS_BASE__TOKEN__VBC__STRING: {\n          if (vbd & WUFFS_BASE__TOKEN__VBD__STRING__CONVERT_0_DST_1_SRC_DROP) {\n            // No-op.\n          } else if (vbd &\n                     WUFFS_BASE__TOKEN__VBD__STRING__CONVERT_1_DST_1_SRC_COPY) {\n            const char* ptr =  // Convert from (uint8_t*).\n                static_cast<const char*>(static_cast<void*>(token_ptr));\n            str.append(ptr, token_len);\n          } else {\n            goto fail;\n          }\n          if (token.continued()) {\n            continue;\n          }\n          ret_error_message =\n              (vbd & WUFFS_BASE__TOKEN__VBD__STRING__CHAIN_MUST_BE_UTF_8)\n                  ? callbacks.AppendTextString(std::move(str))\n                  : callbacks.AppendByteString(std::move(str));\n          str.clear();\n          goto par" +
-	"sed_a_value;\n        }\n\n        case WUFFS_BASE__TOKEN__VBC__UNICODE_CODE_POINT: {\n          uint8_t u[WUFFS_BASE__UTF_8__BYTE_LENGTH__MAX_INCL];\n          size_t n = wuffs_base__utf_8__encode(\n              wuffs_base__make_slice_u8(\n                  &u[0], WUFFS_BASE__UTF_8__BYTE_LENGTH__MAX_INCL),\n              static_cast<uint32_t>(vbd));\n          const char* ptr =  // Convert from (uint8_t*).\n              static_cast<const char*>(static_cast<void*>(&u[0]));\n          str.append(ptr, n);\n          if (token.continued()) {\n            continue;\n          }\n          goto fail;\n        }\n\n        case WUFFS_BASE__TOKEN__VBC__LITERAL: {\n          if (vbd & WUFFS_BASE__TOKEN__VBD__LITERAL__NULL) {\n            ret_error_message = callbacks.AppendNull();\n          } else if (vbd & WUFFS_BASE__TOKEN__VBD__LITERAL__UNDEFINED) {\n            ret_error_message = callbacks.AppendUndefined();\n          } else {\n            ret_error_message = callbacks.AppendBool(\n                vbd & WUFFS_BASE__TOKEN__VBD__LITER" +
-	"AL__TRUE);\n          }\n          goto parsed_a_value;\n        }\n\n        case WUFFS_BASE__TOKEN__VBC__NUMBER: {\n          const uint64_t cfp_fbbe_fifb =\n              WUFFS_BASE__TOKEN__VBD__NUMBER__CONTENT_FLOATING_POINT |\n              WUFFS_BASE__TOKEN__VBD__NUMBER__FORMAT_BINARY_BIG_ENDIAN |\n              WUFFS_BASE__TOKEN__VBD__NUMBER__FORMAT_IGNORE_FIRST_BYTE;\n          if ((vbd & cfp_fbbe_fifb) == cfp_fbbe_fifb) {\n            double f;\n            switch (token_len) {\n              case 3:\n                f = wuffs_base__ieee_754_bit_representation__from_u16_to_f64(\n                    wuffs_base__load_u16be__no_bounds_check(token_ptr + 1));\n                break;\n              case 5:\n                f = wuffs_base__ieee_754_bit_representation__from_u32_to_f64(\n                    wuffs_base__load_u32be__no_bounds_check(token_ptr + 1));\n                break;\n              case 9:\n                f = wuffs_base__ieee_754_bit_representation__from_u64_to_f64(\n                    wuffs_base__load_u64be__" +
-	"no_bounds_check(token_ptr + 1));\n                break;\n              default:\n                goto fail;\n            }\n            ret_error_message = callbacks.AppendF64(f);\n            goto parsed_a_value;\n          }\n          goto fail;\n        }\n\n        case WUFFS_BASE__TOKEN__VBC__INLINE_INTEGER_SIGNED: {\n          if (token.continued()) {\n            extension_category = WUFFS_BASE__TOKEN__VBC__INLINE_INTEGER_SIGNED;\n            extension_detail =\n                static_cast<uint64_t>(token.value_base_detail__sign_extended());\n            continue;\n          }\n          ret_error_message =\n              callbacks.AppendI64(token.value_base_detail__sign_extended());\n          goto parsed_a_value;\n        }\n\n        case WUFFS_BASE__TOKEN__VBC__INLINE_INTEGER_UNSIGNED: {\n          if (token.continued()) {\n            extension_category =\n                WUFFS_BASE__TOKEN__VBC__INLINE_INTEGER_UNSIGNED;\n            extension_detail = vbd;\n            continue;\n          }\n          ret_error_message = ca" +
-	"llbacks.AppendU64(vbd);\n          goto parsed_a_value;\n        }\n      }\n\n      if (token.value_major() == WUFFS_CBOR__TOKEN_VALUE_MAJOR) {\n        uint64_t value_minor = token.value_minor();\n        if (value_minor & WUFFS_CBOR__TOKEN_VALUE_MINOR__MINUS_1_MINUS_X) {\n          if (token_len == 9) {\n            ret_error_message = callbacks.AppendMinus1MinusX(\n                wuffs_base__load_u64be__no_bounds_check(token_ptr + 1));\n            goto parsed_a_value;\n          }\n        } else if (value_minor & WUFFS_CBOR__TOKEN_VALUE_MINOR__SIMPLE_VALUE) {\n          ret_error_message =\n              callbacks.AppendCborSimpleValue(static_cast<uint8_t>(\n                  value_minor & WUFFS_CBOR__TOKEN_VALUE_MINOR__DETAIL_MASK));\n          goto parsed_a_value;\n        } else if (value_minor & WUFFS_CBOR__TOKEN_VALUE_MINOR__TAG) {\n          if (token.continued()) {\n            extension_category = EXT_CAT__CBOR_TAG;\n            extension_detail =\n                value_minor & WUFFS_CBOR__TOKEN_VALUE_MINOR__DETAIL_" +
-	"MASK;\n            continue;\n          }\n          ret_error_message = callbacks.AppendCborTag(\n              value_minor & WUFFS_CBOR__TOKEN_VALUE_MINOR__DETAIL_MASK);\n          if (!ret_error_message.empty()) {\n            goto done;\n          }\n          continue;\n        }\n      }\n\n    fail:\n      ret_error_message =\n          \"wuffs_aux::CborDecoder: internal error: unexpected token\";\n      goto done;\n\n    parsed_a_value:\n      if (!ret_error_message.empty() || (depth == 0)) {\n        goto done;\n      }\n    }\n  } while (false);\n\ndone:\n  DecodeCborResult result(\n      std::move(ret_error_message),\n      wuffs_base__u64__sat_add(io_buf->meta.pos, cursor_index));\n  callbacks.Done(result, input, *io_buf);\n  return result;\n}\n\n}  // namespace wuffs_aux\n\n#endif  // !defined(WUFFS_CONFIG__MODULES) ||\n        // defined(WUFFS_CONFIG__MODULE__AUX__CBOR)\n" +
+	"// ---------------- Auxiliary - CBOR\n\n#if !defined(WUFFS_CONFIG__MODULES) || defined(WUFFS_CONFIG__MODULE__AUX__CBOR)\n\n#include <utility>\n\nnamespace wuffs_aux {\n\nDecodeCborResult::DecodeCborResult(std::string&& error_message0,\n                                   uint64_t cursor_position0)\n    : error_message(std::move(error_message0)),\n      cursor_position(cursor_position0) {}\n\nvoid  //\nDecodeCborCallbacks::Done(DecodeCborResult& result,\n                          sync_io::Input& input,\n                          IOBuffer& buffer) {}\n\nDecodeCborResult  //\nDecodeCbor(DecodeCborCallbacks&& callbacks,\n           sync_io::Input&& input,\n           wuffs_base__slice_u32 quirks) {\n  // Prepare the wuffs_base__io_buffer and the resultant error_message.\n  wuffs_base__io_buffer* io_buf = input.BringsItsOwnIOBuffer();\n  wuffs_base__io_buffer fallback_io_buf = wuffs_base__empty_io_buffer();\n  std::unique_ptr<uint8_t[]> fallback_io_array(nullptr);\n  if (!io_buf) {\n    fallback_io_array = std::unique_ptr<uint8_t[]>(new uint" +
+	"8_t[4096]);\n    fallback_io_buf = wuffs_base__ptr_u8__writer(fallback_io_array.get(), 4096);\n    io_buf = &fallback_io_buf;\n  }\n  size_t cursor_index = 0;\n  std::string ret_error_message;\n  std::string io_error_message;\n\n  do {\n    // Prepare the low-level CBOR decoder.\n    wuffs_cbor__decoder::unique_ptr dec = wuffs_cbor__decoder::alloc();\n    if (!dec) {\n      ret_error_message = \"wuffs_aux::CborDecoder: out of memory\";\n      goto done;\n    }\n    for (size_t i = 0; i < quirks.len; i++) {\n      dec->set_quirk_enabled(quirks.ptr[i], true);\n    }\n\n    // Prepare the wuffs_base__tok_buffer.\n    wuffs_base__token tok_array[256];\n    wuffs_base__token_buffer tok_buf =\n        wuffs_base__slice_token__writer(wuffs_base__make_slice_token(\n            &tok_array[0], (sizeof(tok_array) / sizeof(tok_array[0]))));\n    wuffs_base__status tok_status = wuffs_base__make_status(nullptr);\n\n    // Prepare other state.\n    uint32_t depth = 0;\n    std::string str;\n    int64_t extension_category = 0;\n    uint64_t extension_detai" +
+	"l = 0;\n\n    // Valid token's VBCs range in 0 ..= 15. Values over that are for tokens\n    // from outside of the base package, such as the CBOR package.\n    constexpr int64_t EXT_CAT__CBOR_TAG = 16;\n\n    // Loop, doing these two things:\n    //  1. Get the next token.\n    //  2. Process that token.\n    while (true) {\n      // 1. Get the next token.\n\n      while (tok_buf.meta.ri >= tok_buf.meta.wi) {\n        if (tok_status.repr == nullptr) {\n          // No-op.\n        } else if (tok_status.repr == wuffs_base__suspension__short_write) {\n          tok_buf.compact();\n        } else if (tok_status.repr == wuffs_base__suspension__short_read) {\n          // Read from input to io_buf.\n          if (!io_error_message.empty()) {\n            ret_error_message = std::move(io_error_message);\n            goto done;\n          } else if (cursor_index != io_buf->meta.ri) {\n            ret_error_message =\n                \"wuffs_aux::CborDecoder: internal error: bad cursor_index\";\n            goto done;\n          } else if (io_b" +
+	"uf->meta.closed) {\n            ret_error_message =\n                \"wuffs_aux::CborDecoder: internal error: io_buf is closed\";\n            goto done;\n          }\n          io_buf->compact();\n          if (io_buf->meta.wi >= io_buf->data.len) {\n            ret_error_message =\n                \"wuffs_aux::CborDecoder: internal error: io_buf is full\";\n            goto done;\n          }\n          cursor_index = io_buf->meta.ri;\n          io_error_message = input.CopyIn(io_buf);\n        } else {\n          ret_error_message = tok_status.message();\n          goto done;\n        }\n\n        if (WUFFS_CBOR__DECODER_WORKBUF_LEN_MAX_INCL_WORST_CASE != 0) {\n          ret_error_message =\n              \"wuffs_aux::CborDecoder: internal error: bad WORKBUF_LEN\";\n          goto done;\n        }\n        wuffs_base__slice_u8 work_buf = wuffs_base__empty_slice_u8();\n        tok_status = dec->decode_tokens(&tok_buf, io_buf, work_buf);\n      }\n\n      wuffs_base__token token = tok_buf.data.ptr[tok_buf.meta.ri++];\n      uint64_t token_l" +
+	"en = token.length();\n      if ((io_buf->meta.ri < cursor_index) ||\n          ((io_buf->meta.ri - cursor_index) < token_len)) {\n        ret_error_message =\n            \"wuffs_aux::CborDecoder: internal error: bad token indexes\";\n        goto done;\n      }\n      uint8_t* token_ptr = io_buf->data.ptr + cursor_index;\n      cursor_index += token_len;\n\n      // 2. Process that token.\n\n      uint64_t vbd = token.value_base_detail();\n\n      if (extension_category != 0) {\n        int64_t ext = token.value_extension();\n        if ((ext >= 0) && !token.continued()) {\n          extension_detail = (extension_detail\n                              << WUFFS_BASE__TOKEN__VALUE_EXTENSION__NUM_BITS) |\n                             static_cast<uint64_t>(ext);\n          switch (extension_category) {\n            case WUFFS_BASE__TOKEN__VBC__INLINE_INTEGER_SIGNED:\n              extension_category = 0;\n              ret_error_message =\n                  callbacks.AppendI64(static_cast<int64_t>(extension_detail));\n              goto pa" +
+	"rsed_a_value;\n            case WUFFS_BASE__TOKEN__VBC__INLINE_INTEGER_UNSIGNED:\n              extension_category = 0;\n              ret_error_message = callbacks.AppendU64(extension_detail);\n              goto parsed_a_value;\n            case EXT_CAT__CBOR_TAG:\n              extension_category = 0;\n              ret_error_message = callbacks.AppendCborTag(extension_detail);\n              if (!ret_error_message.empty()) {\n                goto done;\n              }\n              continue;\n          }\n        }\n        ret_error_message =\n            \"wuffs_aux::CborDecoder: internal error: bad extended token\";\n        goto done;\n      }\n\n      switch (token.value_base_category()) {\n        case WUFFS_BASE__TOKEN__VBC__FILLER:\n          continue;\n\n        case WUFFS_BASE__TOKEN__VBC__STRUCTURE: {\n          if (vbd & WUFFS_BASE__TOKEN__VBD__STRUCTURE__PUSH) {\n            ret_error_message = callbacks.Push(static_cast<uint32_t>(vbd));\n            if (!ret_error_message.empty()) {\n              goto done;\n         " +
+	"   }\n            depth++;\n            continue;\n          }\n          ret_error_message = callbacks.Pop(static_cast<uint32_t>(vbd));\n          depth--;\n          goto parsed_a_value;\n        }\n\n        case WUFFS_BASE__TOKEN__VBC__STRING: {\n          if (vbd & WUFFS_BASE__TOKEN__VBD__STRING__CONVERT_0_DST_1_SRC_DROP) {\n            // No-op.\n          } else if (vbd &\n                     WUFFS_BASE__TOKEN__VBD__STRING__CONVERT_1_DST_1_SRC_COPY) {\n            const char* ptr =  // Convert from (uint8_t*).\n                static_cast<const char*>(static_cast<void*>(token_ptr));\n            str.append(ptr, token_len);\n          } else {\n            goto fail;\n          }\n          if (token.continued()) {\n            continue;\n          }\n          ret_error_message =\n              (vbd & WUFFS_BASE__TOKEN__VBD__STRING__CHAIN_MUST_BE_UTF_8)\n                  ? callbacks.AppendTextString(std::move(str))\n                  : callbacks.AppendByteString(std::move(str));\n          str.clear();\n          goto parsed_a_" +
+	"value;\n        }\n\n        case WUFFS_BASE__TOKEN__VBC__UNICODE_CODE_POINT: {\n          uint8_t u[WUFFS_BASE__UTF_8__BYTE_LENGTH__MAX_INCL];\n          size_t n = wuffs_base__utf_8__encode(\n              wuffs_base__make_slice_u8(\n                  &u[0], WUFFS_BASE__UTF_8__BYTE_LENGTH__MAX_INCL),\n              static_cast<uint32_t>(vbd));\n          const char* ptr =  // Convert from (uint8_t*).\n              static_cast<const char*>(static_cast<void*>(&u[0]));\n          str.append(ptr, n);\n          if (token.continued()) {\n            continue;\n          }\n          goto fail;\n        }\n\n        case WUFFS_BASE__TOKEN__VBC__LITERAL: {\n          if (vbd & WUFFS_BASE__TOKEN__VBD__LITERAL__NULL) {\n            ret_error_message = callbacks.AppendNull();\n          } else if (vbd & WUFFS_BASE__TOKEN__VBD__LITERAL__UNDEFINED) {\n            ret_error_message = callbacks.AppendUndefined();\n          } else {\n            ret_error_message = callbacks.AppendBool(\n                vbd & WUFFS_BASE__TOKEN__VBD__LITERAL__TR" +
+	"UE);\n          }\n          goto parsed_a_value;\n        }\n\n        case WUFFS_BASE__TOKEN__VBC__NUMBER: {\n          const uint64_t cfp_fbbe_fifb =\n              WUFFS_BASE__TOKEN__VBD__NUMBER__CONTENT_FLOATING_POINT |\n              WUFFS_BASE__TOKEN__VBD__NUMBER__FORMAT_BINARY_BIG_ENDIAN |\n              WUFFS_BASE__TOKEN__VBD__NUMBER__FORMAT_IGNORE_FIRST_BYTE;\n          if ((vbd & cfp_fbbe_fifb) == cfp_fbbe_fifb) {\n            double f;\n            switch (token_len) {\n              case 3:\n                f = wuffs_base__ieee_754_bit_representation__from_u16_to_f64(\n                    wuffs_base__load_u16be__no_bounds_check(token_ptr + 1));\n                break;\n              case 5:\n                f = wuffs_base__ieee_754_bit_representation__from_u32_to_f64(\n                    wuffs_base__load_u32be__no_bounds_check(token_ptr + 1));\n                break;\n              case 9:\n                f = wuffs_base__ieee_754_bit_representation__from_u64_to_f64(\n                    wuffs_base__load_u64be__no_bou" +
+	"nds_check(token_ptr + 1));\n                break;\n              default:\n                goto fail;\n            }\n            ret_error_message = callbacks.AppendF64(f);\n            goto parsed_a_value;\n          }\n          goto fail;\n        }\n\n        case WUFFS_BASE__TOKEN__VBC__INLINE_INTEGER_SIGNED: {\n          if (token.continued()) {\n            extension_category = WUFFS_BASE__TOKEN__VBC__INLINE_INTEGER_SIGNED;\n            extension_detail =\n                static_cast<uint64_t>(token.value_base_detail__sign_extended());\n            continue;\n          }\n          ret_error_message =\n              callbacks.AppendI64(token.value_base_detail__sign_extended());\n          goto parsed_a_value;\n        }\n\n        case WUFFS_BASE__TOKEN__VBC__INLINE_INTEGER_UNSIGNED: {\n          if (token.continued()) {\n            extension_category =\n                WUFFS_BASE__TOKEN__VBC__INLINE_INTEGER_UNSIGNED;\n            extension_detail = vbd;\n            continue;\n          }\n          ret_error_message = callback" +
+	"s.AppendU64(vbd);\n          goto parsed_a_value;\n        }\n      }\n\n      if (token.value_major() == WUFFS_CBOR__TOKEN_VALUE_MAJOR) {\n        uint64_t value_minor = token.value_minor();\n        if (value_minor & WUFFS_CBOR__TOKEN_VALUE_MINOR__MINUS_1_MINUS_X) {\n          if (token_len == 9) {\n            ret_error_message = callbacks.AppendMinus1MinusX(\n                wuffs_base__load_u64be__no_bounds_check(token_ptr + 1));\n            goto parsed_a_value;\n          }\n        } else if (value_minor & WUFFS_CBOR__TOKEN_VALUE_MINOR__SIMPLE_VALUE) {\n          ret_error_message =\n              callbacks.AppendCborSimpleValue(static_cast<uint8_t>(\n                  value_minor & WUFFS_CBOR__TOKEN_VALUE_MINOR__DETAIL_MASK));\n          goto parsed_a_value;\n        } else if (value_minor & WUFFS_CBOR__TOKEN_VALUE_MINOR__TAG) {\n          if (token.continued()) {\n            extension_category = EXT_CAT__CBOR_TAG;\n            extension_detail =\n                value_minor & WUFFS_CBOR__TOKEN_VALUE_MINOR__DETAIL_MASK;\n" +
+	"            continue;\n          }\n          ret_error_message = callbacks.AppendCborTag(\n              value_minor & WUFFS_CBOR__TOKEN_VALUE_MINOR__DETAIL_MASK);\n          if (!ret_error_message.empty()) {\n            goto done;\n          }\n          continue;\n        }\n      }\n\n    fail:\n      ret_error_message =\n          \"wuffs_aux::CborDecoder: internal error: unexpected token\";\n      goto done;\n\n    parsed_a_value:\n      if (!ret_error_message.empty() || (depth == 0)) {\n        goto done;\n      }\n    }\n  } while (false);\n\ndone:\n  DecodeCborResult result(\n      std::move(ret_error_message),\n      wuffs_base__u64__sat_add(io_buf->meta.pos, cursor_index));\n  callbacks.Done(result, input, *io_buf);\n  return result;\n}\n\n}  // namespace wuffs_aux\n\n#endif  // !defined(WUFFS_CONFIG__MODULES) ||\n        // defined(WUFFS_CONFIG__MODULE__AUX__CBOR)\n" +
 	""
 
 const AuxCborHh = "" +
 	"// ---------------- Auxiliary - CBOR\n\nnamespace wuffs_aux {\n\nstruct DecodeCborResult {\n  DecodeCborResult(std::string&& error_message0, uint64_t cursor_position0);\n\n  std::string error_message;\n  uint64_t cursor_position;\n};\n\nclass DecodeCborCallbacks {\n public:\n  // AppendXxx are called for leaf nodes: literals, numbers, strings, etc.\n\n  virtual std::string AppendNull() = 0;\n  virtual std::string AppendUndefined() = 0;\n  virtual std::string AppendBool(bool val) = 0;\n  virtual std::string AppendF64(double val) = 0;\n  virtual std::string AppendI64(int64_t val) = 0;\n  virtual std::string AppendU64(uint64_t val) = 0;\n  virtual std::string AppendByteString(std::string&& val) = 0;\n  virtual std::string AppendTextString(std::string&& val) = 0;\n  virtual std::string AppendMinus1MinusX(uint64_t val) = 0;\n  virtual std::string AppendCborSimpleValue(uint8_t val) = 0;\n  virtual std::string AppendCborTag(uint64_t val) = 0;\n\n  // Push and Pop are called for container nodes: CBOR arrays (lists) and CBOR\n  // maps (dictiona" +
-	"ries).\n  //\n  // The flags bits combine exactly one of:\n  //  - WUFFS_BASE__TOKEN__VBD__STRUCTURE__FROM_NONE\n  //  - WUFFS_BASE__TOKEN__VBD__STRUCTURE__FROM_LIST\n  //  - WUFFS_BASE__TOKEN__VBD__STRUCTURE__FROM_DICT\n  // and exactly one of:\n  //  - WUFFS_BASE__TOKEN__VBD__STRUCTURE__TO_NONE\n  //  - WUFFS_BASE__TOKEN__VBD__STRUCTURE__TO_LIST\n  //  - WUFFS_BASE__TOKEN__VBD__STRUCTURE__TO_DICT\n\n  virtual std::string Push(uint32_t flags) = 0;\n  virtual std::string Pop(uint32_t flags) = 0;\n\n  // Done is always the last Callback method called by DecodeCbor, whether or\n  // not parsing the input as CBOR encountered an error. Even when successful,\n  // trailing data may remain in input and buffer.\n  //\n  // Do not keep a reference to buffer or buffer.data.ptr after Done returns,\n  // as DecodeCbor may then de-allocate the backing array.\n  virtual void Done(DecodeCborResult& result,\n                    sync_io::Input& input,\n                    IOBuffer& buffer);\n};\n\n// DecodeCbor calls callbacks based on the CBOR-form" +
-	"atted data in input.\n//\n// On success, the returned error_message is empty and cursor_position counts\n// the number of bytes consumed. On failure, error_message is non-empty and\n// cursor_position is the location of the error. That error may be a content\n// error (invalid CBOR) or an input error (e.g. network failure).\nDecodeCborResult DecodeCbor(DecodeCborCallbacks&& callbacks,\n                            sync_io::Input&& input,\n                            wuffs_base__slice_u32 quirks);\n\n}  // namespace wuffs_aux\n" +
+	"ries).\n  //\n  // The flags bits combine exactly one of:\n  //  - WUFFS_BASE__TOKEN__VBD__STRUCTURE__FROM_NONE\n  //  - WUFFS_BASE__TOKEN__VBD__STRUCTURE__FROM_LIST\n  //  - WUFFS_BASE__TOKEN__VBD__STRUCTURE__FROM_DICT\n  // and exactly one of:\n  //  - WUFFS_BASE__TOKEN__VBD__STRUCTURE__TO_NONE\n  //  - WUFFS_BASE__TOKEN__VBD__STRUCTURE__TO_LIST\n  //  - WUFFS_BASE__TOKEN__VBD__STRUCTURE__TO_DICT\n\n  virtual std::string Push(uint32_t flags) = 0;\n  virtual std::string Pop(uint32_t flags) = 0;\n\n  // Done is always the last Callback method called by DecodeCbor, whether or\n  // not parsing the input as CBOR encountered an error. Even when successful,\n  // trailing data may remain in input and buffer.\n  //\n  // Do not keep a reference to buffer or buffer.data.ptr after Done returns,\n  // as DecodeCbor may then de-allocate the backing array.\n  //\n  // The default Done implementation is a no-op.\n  virtual void Done(DecodeCborResult& result,\n                    sync_io::Input& input,\n                    IOBuffer& buffer);\n};" +
+	"\n\n// DecodeCbor calls callbacks based on the CBOR-formatted data in input.\n//\n// On success, the returned error_message is empty and cursor_position counts\n// the number of bytes consumed. On failure, error_message is non-empty and\n// cursor_position is the location of the error. That error may be a content\n// error (invalid CBOR) or an input error (e.g. network failure).\nDecodeCborResult DecodeCbor(DecodeCborCallbacks&& callbacks,\n                            sync_io::Input&& input,\n                            wuffs_base__slice_u32 quirks);\n\n}  // namespace wuffs_aux\n" +
 	""
 
 const AuxJsonCc = "" +
-	"// ---------------- Auxiliary - JSON\n\n#if !defined(WUFFS_CONFIG__MODULES) || defined(WUFFS_CONFIG__MODULE__AUX__JSON)\n\n#include <utility>\n\nnamespace wuffs_aux {\n\nDecodeJsonResult::DecodeJsonResult(std::string&& error_message0,\n                                   uint64_t cursor_position0)\n    : error_message(std::move(error_message0)),\n      cursor_position(cursor_position0) {}\n\nvoid DecodeJsonCallbacks::Done(DecodeJsonResult& result,\n                               sync_io::Input& input,\n                               IOBuffer& buffer) {}\n\nDecodeJsonResult  //\nDecodeJson(DecodeJsonCallbacks&& callbacks,\n           sync_io::Input&& input,\n           wuffs_base__slice_u32 quirks) {\n  // Prepare the wuffs_base__io_buffer and the resultant error_message.\n  wuffs_base__io_buffer* io_buf = input.BringsItsOwnIOBuffer();\n  wuffs_base__io_buffer fallback_io_buf = wuffs_base__empty_io_buffer();\n  std::unique_ptr<uint8_t[]> fallback_io_array(nullptr);\n  if (!io_buf) {\n    fallback_io_array = std::unique_ptr<uint8_t[]>(ne" +
-	"w uint8_t[4096]);\n    fallback_io_buf = wuffs_base__ptr_u8__writer(fallback_io_array.get(), 4096);\n    io_buf = &fallback_io_buf;\n  }\n  size_t cursor_index = 0;\n  std::string ret_error_message;\n  std::string io_error_message;\n\n  do {\n    // Prepare the low-level JSON decoder.\n    wuffs_json__decoder::unique_ptr dec = wuffs_json__decoder::alloc();\n    if (!dec) {\n      ret_error_message = \"wuffs_aux::JsonDecoder: out of memory\";\n      goto done;\n    }\n    for (size_t i = 0; i < quirks.len; i++) {\n      dec->set_quirk_enabled(quirks.ptr[i], true);\n    }\n\n    // Prepare the wuffs_base__tok_buffer.\n    wuffs_base__token tok_array[256];\n    wuffs_base__token_buffer tok_buf =\n        wuffs_base__slice_token__writer(wuffs_base__make_slice_token(\n            &tok_array[0], (sizeof(tok_array) / sizeof(tok_array[0]))));\n    wuffs_base__status tok_status = wuffs_base__make_status(nullptr);\n\n    // Prepare other state.\n    uint32_t depth = 0;\n    std::string str;\n\n    // Loop, doing these two things:\n    //  1. Get the n" +
-	"ext token.\n    //  2. Process that token.\n    while (true) {\n      // 1. Get the next token.\n\n      while (tok_buf.meta.ri >= tok_buf.meta.wi) {\n        if (tok_status.repr == nullptr) {\n          // No-op.\n        } else if (tok_status.repr == wuffs_base__suspension__short_write) {\n          tok_buf.compact();\n        } else if (tok_status.repr == wuffs_base__suspension__short_read) {\n          // Read from input to io_buf.\n          if (!io_error_message.empty()) {\n            ret_error_message = std::move(io_error_message);\n            goto done;\n          } else if (cursor_index != io_buf->meta.ri) {\n            ret_error_message =\n                \"wuffs_aux::JsonDecoder: internal error: bad cursor_index\";\n            goto done;\n          } else if (io_buf->meta.closed) {\n            ret_error_message =\n                \"wuffs_aux::JsonDecoder: internal error: io_buf is closed\";\n            goto done;\n          }\n          io_buf->compact();\n          if (io_buf->meta.wi >= io_buf->data.len) {\n            " +
-	"ret_error_message =\n                \"wuffs_aux::JsonDecoder: internal error: io_buf is full\";\n            goto done;\n          }\n          cursor_index = io_buf->meta.ri;\n          io_error_message = input.CopyIn(io_buf);\n        } else {\n          ret_error_message = tok_status.message();\n          goto done;\n        }\n\n        if (WUFFS_JSON__DECODER_WORKBUF_LEN_MAX_INCL_WORST_CASE != 0) {\n          ret_error_message =\n              \"wuffs_aux::JsonDecoder: internal error: bad WORKBUF_LEN\";\n          goto done;\n        }\n        wuffs_base__slice_u8 work_buf = wuffs_base__empty_slice_u8();\n        tok_status = dec->decode_tokens(&tok_buf, io_buf, work_buf);\n      }\n\n      wuffs_base__token token = tok_buf.data.ptr[tok_buf.meta.ri++];\n      uint64_t token_len = token.length();\n      if ((io_buf->meta.ri < cursor_index) ||\n          ((io_buf->meta.ri - cursor_index) < token_len)) {\n        ret_error_message =\n            \"wuffs_aux::JsonDecoder: internal error: bad token indexes\";\n        goto done;\n      }\n " +
-	"     uint8_t* token_ptr = io_buf->data.ptr + cursor_index;\n      cursor_index += token_len;\n\n      // 2. Process that token.\n\n      int64_t vbc = token.value_base_category();\n      uint64_t vbd = token.value_base_detail();\n      switch (vbc) {\n        case WUFFS_BASE__TOKEN__VBC__FILLER:\n          continue;\n\n        case WUFFS_BASE__TOKEN__VBC__STRUCTURE: {\n          if (vbd & WUFFS_BASE__TOKEN__VBD__STRUCTURE__PUSH) {\n            ret_error_message = callbacks.Push(static_cast<uint32_t>(vbd));\n            if (!ret_error_message.empty()) {\n              goto done;\n            }\n            depth++;\n            continue;\n          }\n          ret_error_message = callbacks.Pop(static_cast<uint32_t>(vbd));\n          depth--;\n          goto parsed_a_value;\n        }\n\n        case WUFFS_BASE__TOKEN__VBC__STRING: {\n          if (vbd & WUFFS_BASE__TOKEN__VBD__STRING__CONVERT_0_DST_1_SRC_DROP) {\n            // No-op.\n          } else if (vbd &\n                     WUFFS_BASE__TOKEN__VBD__STRING__CONVERT_1_DST_1_SRC_CO" +
-	"PY) {\n            const char* ptr =  // Convert from (uint8_t*).\n                static_cast<const char*>(static_cast<void*>(token_ptr));\n            str.append(ptr, token_len);\n          } else {\n            goto fail;\n          }\n          if (token.continued()) {\n            continue;\n          }\n          ret_error_message = callbacks.AppendTextString(std::move(str));\n          str.clear();\n          goto parsed_a_value;\n        }\n\n        case WUFFS_BASE__TOKEN__VBC__UNICODE_CODE_POINT: {\n          uint8_t u[WUFFS_BASE__UTF_8__BYTE_LENGTH__MAX_INCL];\n          size_t n = wuffs_base__utf_8__encode(\n              wuffs_base__make_slice_u8(\n                  &u[0], WUFFS_BASE__UTF_8__BYTE_LENGTH__MAX_INCL),\n              static_cast<uint32_t>(vbd));\n          const char* ptr =  // Convert from (uint8_t*).\n              static_cast<const char*>(static_cast<void*>(&u[0]));\n          str.append(ptr, n);\n          if (token.continued()) {\n            continue;\n          }\n          goto fail;\n        }\n\n       " +
-	" case WUFFS_BASE__TOKEN__VBC__LITERAL: {\n          ret_error_message =\n              (vbd & WUFFS_BASE__TOKEN__VBD__LITERAL__NULL)\n                  ? callbacks.AppendNull()\n                  : callbacks.AppendBool(vbd &\n                                         WUFFS_BASE__TOKEN__VBD__LITERAL__TRUE);\n          goto parsed_a_value;\n        }\n\n        case WUFFS_BASE__TOKEN__VBC__NUMBER: {\n          if (vbd & WUFFS_BASE__TOKEN__VBD__NUMBER__FORMAT_TEXT) {\n            if (vbd & WUFFS_BASE__TOKEN__VBD__NUMBER__CONTENT_INTEGER_SIGNED) {\n              wuffs_base__result_i64 r = wuffs_base__parse_number_i64(\n                  wuffs_base__make_slice_u8(token_ptr, token_len),\n                  WUFFS_BASE__PARSE_NUMBER_XXX__DEFAULT_OPTIONS);\n              if (r.status.is_ok()) {\n                ret_error_message = callbacks.AppendI64(r.value);\n                goto parsed_a_value;\n              }\n            }\n            if (vbd & WUFFS_BASE__TOKEN__VBD__NUMBER__CONTENT_FLOATING_POINT) {\n              wuffs_base__resul" +
-	"t_f64 r = wuffs_base__parse_number_f64(\n                  wuffs_base__make_slice_u8(token_ptr, token_len),\n                  WUFFS_BASE__PARSE_NUMBER_XXX__DEFAULT_OPTIONS);\n              if (r.status.is_ok()) {\n                ret_error_message = callbacks.AppendF64(r.value);\n                goto parsed_a_value;\n              }\n            }\n          } else if (vbd & WUFFS_BASE__TOKEN__VBD__NUMBER__CONTENT_NEG_INF) {\n            ret_error_message = callbacks.AppendF64(\n                wuffs_base__ieee_754_bit_representation__from_u64_to_f64(\n                    0xFFF0000000000000ul));\n            goto parsed_a_value;\n          } else if (vbd & WUFFS_BASE__TOKEN__VBD__NUMBER__CONTENT_POS_INF) {\n            ret_error_message = callbacks.AppendF64(\n                wuffs_base__ieee_754_bit_representation__from_u64_to_f64(\n                    0x7FF0000000000000ul));\n            goto parsed_a_value;\n          } else if (vbd & WUFFS_BASE__TOKEN__VBD__NUMBER__CONTENT_NEG_NAN) {\n            ret_error_message = callba" +
-	"cks.AppendF64(\n                wuffs_base__ieee_754_bit_representation__from_u64_to_f64(\n                    0xFFFFFFFFFFFFFFFFul));\n            goto parsed_a_value;\n          } else if (vbd & WUFFS_BASE__TOKEN__VBD__NUMBER__CONTENT_POS_NAN) {\n            ret_error_message = callbacks.AppendF64(\n                wuffs_base__ieee_754_bit_representation__from_u64_to_f64(\n                    0x7FFFFFFFFFFFFFFFul));\n            goto parsed_a_value;\n          }\n          goto fail;\n        }\n      }\n\n    fail:\n      ret_error_message =\n          \"wuffs_aux::JsonDecoder: internal error: unexpected token\";\n      goto done;\n\n    parsed_a_value:\n      if (!ret_error_message.empty() || (depth == 0)) {\n        goto done;\n      }\n    }\n  } while (false);\n\ndone:\n  DecodeJsonResult result(\n      std::move(ret_error_message),\n      wuffs_base__u64__sat_add(io_buf->meta.pos, cursor_index));\n  callbacks.Done(result, input, *io_buf);\n  return result;\n}\n\n}  // namespace wuffs_aux\n\n#endif  // !defined(WUFFS_CONFIG__MODULES) ||\n  " +
-	"      // defined(WUFFS_CONFIG__MODULE__AUX__JSON)\n" +
+	"// ---------------- Auxiliary - JSON\n\n#if !defined(WUFFS_CONFIG__MODULES) || defined(WUFFS_CONFIG__MODULE__AUX__JSON)\n\n#include <utility>\n\nnamespace wuffs_aux {\n\nDecodeJsonResult::DecodeJsonResult(std::string&& error_message0,\n                                   uint64_t cursor_position0)\n    : error_message(std::move(error_message0)),\n      cursor_position(cursor_position0) {}\n\nstd::string  //\nDecodeJsonCallbacks::AppendByteString(std::string&& val) {\n  return \"wuffs_aux::JsonDecoder: unexpected JSON byte string\";\n}\n\nvoid  //\nDecodeJsonCallbacks::Done(DecodeJsonResult& result,\n                          sync_io::Input& input,\n                          IOBuffer& buffer) {}\n\nDecodeJsonResult  //\nDecodeJson(DecodeJsonCallbacks&& callbacks,\n           sync_io::Input&& input,\n           wuffs_base__slice_u32 quirks) {\n  // Prepare the wuffs_base__io_buffer and the resultant error_message.\n  wuffs_base__io_buffer* io_buf = input.BringsItsOwnIOBuffer();\n  wuffs_base__io_buffer fallback_io_buf = wuffs_base__empty_io_b" +
+	"uffer();\n  std::unique_ptr<uint8_t[]> fallback_io_array(nullptr);\n  if (!io_buf) {\n    fallback_io_array = std::unique_ptr<uint8_t[]>(new uint8_t[4096]);\n    fallback_io_buf = wuffs_base__ptr_u8__writer(fallback_io_array.get(), 4096);\n    io_buf = &fallback_io_buf;\n  }\n  size_t cursor_index = 0;\n  std::string ret_error_message;\n  std::string io_error_message;\n\n  do {\n    // Prepare the low-level JSON decoder.\n    wuffs_json__decoder::unique_ptr dec = wuffs_json__decoder::alloc();\n    if (!dec) {\n      ret_error_message = \"wuffs_aux::JsonDecoder: out of memory\";\n      goto done;\n    }\n    for (size_t i = 0; i < quirks.len; i++) {\n      dec->set_quirk_enabled(quirks.ptr[i], true);\n    }\n\n    // Prepare the wuffs_base__tok_buffer.\n    wuffs_base__token tok_array[256];\n    wuffs_base__token_buffer tok_buf =\n        wuffs_base__slice_token__writer(wuffs_base__make_slice_token(\n            &tok_array[0], (sizeof(tok_array) / sizeof(tok_array[0]))));\n    wuffs_base__status tok_status = wuffs_base__make_status(nullpt" +
+	"r);\n\n    // Prepare other state.\n    uint32_t depth = 0;\n    std::string str;\n\n    // Loop, doing these two things:\n    //  1. Get the next token.\n    //  2. Process that token.\n    while (true) {\n      // 1. Get the next token.\n\n      while (tok_buf.meta.ri >= tok_buf.meta.wi) {\n        if (tok_status.repr == nullptr) {\n          // No-op.\n        } else if (tok_status.repr == wuffs_base__suspension__short_write) {\n          tok_buf.compact();\n        } else if (tok_status.repr == wuffs_base__suspension__short_read) {\n          // Read from input to io_buf.\n          if (!io_error_message.empty()) {\n            ret_error_message = std::move(io_error_message);\n            goto done;\n          } else if (cursor_index != io_buf->meta.ri) {\n            ret_error_message =\n                \"wuffs_aux::JsonDecoder: internal error: bad cursor_index\";\n            goto done;\n          } else if (io_buf->meta.closed) {\n            ret_error_message =\n                \"wuffs_aux::JsonDecoder: internal error: io_buf is cl" +
+	"osed\";\n            goto done;\n          }\n          io_buf->compact();\n          if (io_buf->meta.wi >= io_buf->data.len) {\n            ret_error_message =\n                \"wuffs_aux::JsonDecoder: internal error: io_buf is full\";\n            goto done;\n          }\n          cursor_index = io_buf->meta.ri;\n          io_error_message = input.CopyIn(io_buf);\n        } else {\n          ret_error_message = tok_status.message();\n          goto done;\n        }\n\n        if (WUFFS_JSON__DECODER_WORKBUF_LEN_MAX_INCL_WORST_CASE != 0) {\n          ret_error_message =\n              \"wuffs_aux::JsonDecoder: internal error: bad WORKBUF_LEN\";\n          goto done;\n        }\n        wuffs_base__slice_u8 work_buf = wuffs_base__empty_slice_u8();\n        tok_status = dec->decode_tokens(&tok_buf, io_buf, work_buf);\n      }\n\n      wuffs_base__token token = tok_buf.data.ptr[tok_buf.meta.ri++];\n      uint64_t token_len = token.length();\n      if ((io_buf->meta.ri < cursor_index) ||\n          ((io_buf->meta.ri - cursor_index) < token_l" +
+	"en)) {\n        ret_error_message =\n            \"wuffs_aux::JsonDecoder: internal error: bad token indexes\";\n        goto done;\n      }\n      uint8_t* token_ptr = io_buf->data.ptr + cursor_index;\n      cursor_index += token_len;\n\n      // 2. Process that token.\n\n      int64_t vbc = token.value_base_category();\n      uint64_t vbd = token.value_base_detail();\n      switch (vbc) {\n        case WUFFS_BASE__TOKEN__VBC__FILLER:\n          continue;\n\n        case WUFFS_BASE__TOKEN__VBC__STRUCTURE: {\n          if (vbd & WUFFS_BASE__TOKEN__VBD__STRUCTURE__PUSH) {\n            ret_error_message = callbacks.Push(static_cast<uint32_t>(vbd));\n            if (!ret_error_message.empty()) {\n              goto done;\n            }\n            depth++;\n            continue;\n          }\n          ret_error_message = callbacks.Pop(static_cast<uint32_t>(vbd));\n          depth--;\n          goto parsed_a_value;\n        }\n\n        case WUFFS_BASE__TOKEN__VBC__STRING: {\n          if (vbd & WUFFS_BASE__TOKEN__VBD__STRING__CONVERT_0_DST_1_" +
+	"SRC_DROP) {\n            // No-op.\n          } else if (vbd &\n                     WUFFS_BASE__TOKEN__VBD__STRING__CONVERT_1_DST_1_SRC_COPY) {\n            const char* ptr =  // Convert from (uint8_t*).\n                static_cast<const char*>(static_cast<void*>(token_ptr));\n            str.append(ptr, token_len);\n          } else if (\n              vbd &\n              WUFFS_BASE__TOKEN__VBD__STRING__CONVERT_1_DST_4_SRC_BACKSLASH_X) {\n            wuffs_base__slice_u8 encoded =\n                wuffs_base__make_slice_u8(token_ptr, token_len);\n            while (encoded.len > 0) {\n              uint8_t decoded[64];\n              constexpr bool src_closed = true;\n              wuffs_base__transform__output o = wuffs_base__base_16__decode4(\n                  wuffs_base__make_slice_u8(&decoded[0], sizeof decoded),\n                  encoded, src_closed, WUFFS_BASE__BASE_16__DEFAULT_OPTIONS);\n              if (o.status.is_error()) {\n                ret_error_message = o.status.message();\n                goto done;\n    " +
+	"          } else if ((o.num_dst > (sizeof decoded)) ||\n                         (o.num_src > encoded.len)) {\n                ret_error_message =\n                    \"wuffs_aux::JsonDecoder: internal error: inconsistent \"\n                    \"base16 decoding\";\n                goto done;\n              }\n              str.append(  // Convert from (uint8_t*).\n                  static_cast<const char*>(static_cast<void*>(&decoded[0])),\n                  o.num_dst);\n              encoded.ptr += o.num_src;\n              encoded.len -= o.num_src;\n            }\n          } else {\n            goto fail;\n          }\n          if (token.continued()) {\n            continue;\n          }\n          ret_error_message =\n              (vbd & WUFFS_BASE__TOKEN__VBD__STRING__CHAIN_MUST_BE_UTF_8)\n                  ? callbacks.AppendTextString(std::move(str))\n                  : callbacks.AppendByteString(std::move(str));\n          str.clear();\n          goto parsed_a_value;\n        }\n\n        case WUFFS_BASE__TOKEN__VBC__UNICODE_C" +
+	"ODE_POINT: {\n          uint8_t u[WUFFS_BASE__UTF_8__BYTE_LENGTH__MAX_INCL];\n          size_t n = wuffs_base__utf_8__encode(\n              wuffs_base__make_slice_u8(\n                  &u[0], WUFFS_BASE__UTF_8__BYTE_LENGTH__MAX_INCL),\n              static_cast<uint32_t>(vbd));\n          const char* ptr =  // Convert from (uint8_t*).\n              static_cast<const char*>(static_cast<void*>(&u[0]));\n          str.append(ptr, n);\n          if (token.continued()) {\n            continue;\n          }\n          goto fail;\n        }\n\n        case WUFFS_BASE__TOKEN__VBC__LITERAL: {\n          ret_error_message =\n              (vbd & WUFFS_BASE__TOKEN__VBD__LITERAL__NULL)\n                  ? callbacks.AppendNull()\n                  : callbacks.AppendBool(vbd &\n                                         WUFFS_BASE__TOKEN__VBD__LITERAL__TRUE);\n          goto parsed_a_value;\n        }\n\n        case WUFFS_BASE__TOKEN__VBC__NUMBER: {\n          if (vbd & WUFFS_BASE__TOKEN__VBD__NUMBER__FORMAT_TEXT) {\n            if (vbd & WUFFS_" +
+	"BASE__TOKEN__VBD__NUMBER__CONTENT_INTEGER_SIGNED) {\n              wuffs_base__result_i64 r = wuffs_base__parse_number_i64(\n                  wuffs_base__make_slice_u8(token_ptr, token_len),\n                  WUFFS_BASE__PARSE_NUMBER_XXX__DEFAULT_OPTIONS);\n              if (r.status.is_ok()) {\n                ret_error_message = callbacks.AppendI64(r.value);\n                goto parsed_a_value;\n              }\n            }\n            if (vbd & WUFFS_BASE__TOKEN__VBD__NUMBER__CONTENT_FLOATING_POINT) {\n              wuffs_base__result_f64 r = wuffs_base__parse_number_f64(\n                  wuffs_base__make_slice_u8(token_ptr, token_len),\n                  WUFFS_BASE__PARSE_NUMBER_XXX__DEFAULT_OPTIONS);\n              if (r.status.is_ok()) {\n                ret_error_message = callbacks.AppendF64(r.value);\n                goto parsed_a_value;\n              }\n            }\n          } else if (vbd & WUFFS_BASE__TOKEN__VBD__NUMBER__CONTENT_NEG_INF) {\n            ret_error_message = callbacks.AppendF64(\n           " +
+	"     wuffs_base__ieee_754_bit_representation__from_u64_to_f64(\n                    0xFFF0000000000000ul));\n            goto parsed_a_value;\n          } else if (vbd & WUFFS_BASE__TOKEN__VBD__NUMBER__CONTENT_POS_INF) {\n            ret_error_message = callbacks.AppendF64(\n                wuffs_base__ieee_754_bit_representation__from_u64_to_f64(\n                    0x7FF0000000000000ul));\n            goto parsed_a_value;\n          } else if (vbd & WUFFS_BASE__TOKEN__VBD__NUMBER__CONTENT_NEG_NAN) {\n            ret_error_message = callbacks.AppendF64(\n                wuffs_base__ieee_754_bit_representation__from_u64_to_f64(\n                    0xFFFFFFFFFFFFFFFFul));\n            goto parsed_a_value;\n          } else if (vbd & WUFFS_BASE__TOKEN__VBD__NUMBER__CONTENT_POS_NAN) {\n            ret_error_message = callbacks.AppendF64(\n                wuffs_base__ieee_754_bit_representation__from_u64_to_f64(\n                    0x7FFFFFFFFFFFFFFFul));\n            goto parsed_a_value;\n          }\n          goto fail;\n     " +
+	"   }\n      }\n\n    fail:\n      ret_error_message =\n          \"wuffs_aux::JsonDecoder: internal error: unexpected token\";\n      goto done;\n\n    parsed_a_value:\n      if (!ret_error_message.empty() || (depth == 0)) {\n        goto done;\n      }\n    }\n  } while (false);\n\ndone:\n  DecodeJsonResult result(\n      std::move(ret_error_message),\n      wuffs_base__u64__sat_add(io_buf->meta.pos, cursor_index));\n  callbacks.Done(result, input, *io_buf);\n  return result;\n}\n\n}  // namespace wuffs_aux\n\n#endif  // !defined(WUFFS_CONFIG__MODULES) ||\n        // defined(WUFFS_CONFIG__MODULE__AUX__JSON)\n" +
 	""
 
 const AuxJsonHh = "" +
-	"// ---------------- Auxiliary - JSON\n\nnamespace wuffs_aux {\n\nstruct DecodeJsonResult {\n  DecodeJsonResult(std::string&& error_message0, uint64_t cursor_position0);\n\n  std::string error_message;\n  uint64_t cursor_position;\n};\n\nclass DecodeJsonCallbacks {\n public:\n  // AppendXxx are called for leaf nodes: literals, numbers and strings. For\n  // strings, the Callbacks implementation is responsible for tracking map keys\n  // versus other values.\n\n  virtual std::string AppendNull() = 0;\n  virtual std::string AppendBool(bool val) = 0;\n  virtual std::string AppendF64(double val) = 0;\n  virtual std::string AppendI64(int64_t val) = 0;\n  virtual std::string AppendTextString(std::string&& val) = 0;\n\n  // Push and Pop are called for container nodes: JSON arrays (lists) and JSON\n  // objects (dictionaries).\n  //\n  // The flags bits combine exactly one of:\n  //  - WUFFS_BASE__TOKEN__VBD__STRUCTURE__FROM_NONE\n  //  - WUFFS_BASE__TOKEN__VBD__STRUCTURE__FROM_LIST\n  //  - WUFFS_BASE__TOKEN__VBD__STRUCTURE__FROM_DICT\n  // and e" +
-	"xactly one of:\n  //  - WUFFS_BASE__TOKEN__VBD__STRUCTURE__TO_NONE\n  //  - WUFFS_BASE__TOKEN__VBD__STRUCTURE__TO_LIST\n  //  - WUFFS_BASE__TOKEN__VBD__STRUCTURE__TO_DICT\n\n  virtual std::string Push(uint32_t flags) = 0;\n  virtual std::string Pop(uint32_t flags) = 0;\n\n  // Done is always the last Callback method called by DecodeJson, whether or\n  // not parsing the input as JSON encountered an error. Even when successful,\n  // trailing data may remain in input and buffer. See \"Unintuitive JSON\n  // Parsing\" (https://nullprogram.com/blog/2019/12/28/) which discusses JSON\n  // parsing and when it stops.\n  //\n  // Do not keep a reference to buffer or buffer.data.ptr after Done returns,\n  // as DecodeJson may then de-allocate the backing array.\n  virtual void Done(DecodeJsonResult& result,\n                    sync_io::Input& input,\n                    IOBuffer& buffer);\n};\n\n// DecodeJson calls callbacks based on the JSON-formatted data in input.\n//\n// On success, the returned error_message is empty and cursor_positio" +
-	"n counts\n// the number of bytes consumed. On failure, error_message is non-empty and\n// cursor_position is the location of the error. That error may be a content\n// error (invalid JSON) or an input error (e.g. network failure).\nDecodeJsonResult DecodeJson(DecodeJsonCallbacks&& callbacks,\n                            sync_io::Input&& input,\n                            wuffs_base__slice_u32 quirks);\n\n}  // namespace wuffs_aux\n" +
+	"// ---------------- Auxiliary - JSON\n\nnamespace wuffs_aux {\n\nstruct DecodeJsonResult {\n  DecodeJsonResult(std::string&& error_message0, uint64_t cursor_position0);\n\n  std::string error_message;\n  uint64_t cursor_position;\n};\n\nclass DecodeJsonCallbacks {\n public:\n  // AppendXxx are called for leaf nodes: literals, numbers and strings. For\n  // strings, the Callbacks implementation is responsible for tracking map keys\n  // versus other values.\n\n  // The JSON file format as specified deals only with (UTF-8) text strings,\n  // but an unofficial extension allows \"ijk\\x89m\" escapes within those\n  // strings. DecodeJsonCallbacks' AppendByteString will not be called unless\n  // WUFFS_JSON__QUIRK_ALLOW_BACKSLASH_X_AS_BYTES is passed to DecodeJson. If\n  // it is passed, AppendTextString will not be called and all byte strings are\n  // potentially invalid UTF-8. It is up to the AppendByteString implementation\n  // whether to test the std::string for UTF-8 validity.\n  //\n  // The default AppendByteString implementation r" +
+	"eturns an error message.\n\n  virtual std::string AppendNull() = 0;\n  virtual std::string AppendBool(bool val) = 0;\n  virtual std::string AppendF64(double val) = 0;\n  virtual std::string AppendI64(int64_t val) = 0;\n  virtual std::string AppendByteString(std::string&& val);\n  virtual std::string AppendTextString(std::string&& val) = 0;\n\n  // Push and Pop are called for container nodes: JSON arrays (lists) and JSON\n  // objects (dictionaries).\n  //\n  // The flags bits combine exactly one of:\n  //  - WUFFS_BASE__TOKEN__VBD__STRUCTURE__FROM_NONE\n  //  - WUFFS_BASE__TOKEN__VBD__STRUCTURE__FROM_LIST\n  //  - WUFFS_BASE__TOKEN__VBD__STRUCTURE__FROM_DICT\n  // and exactly one of:\n  //  - WUFFS_BASE__TOKEN__VBD__STRUCTURE__TO_NONE\n  //  - WUFFS_BASE__TOKEN__VBD__STRUCTURE__TO_LIST\n  //  - WUFFS_BASE__TOKEN__VBD__STRUCTURE__TO_DICT\n\n  virtual std::string Push(uint32_t flags) = 0;\n  virtual std::string Pop(uint32_t flags) = 0;\n\n  // Done is always the last Callback method called by DecodeJson, whether or\n  // not parsing th" +
+	"e input as JSON encountered an error. Even when successful,\n  // trailing data may remain in input and buffer. See \"Unintuitive JSON\n  // Parsing\" (https://nullprogram.com/blog/2019/12/28/) which discusses JSON\n  // parsing and when it stops.\n  //\n  // Do not keep a reference to buffer or buffer.data.ptr after Done returns,\n  // as DecodeJson may then de-allocate the backing array.\n  //\n  // The default Done implementation is a no-op.\n  virtual void Done(DecodeJsonResult& result,\n                    sync_io::Input& input,\n                    IOBuffer& buffer);\n};\n\n// DecodeJson calls callbacks based on the JSON-formatted data in input.\n//\n// On success, the returned error_message is empty and cursor_position counts\n// the number of bytes consumed. On failure, error_message is non-empty and\n// cursor_position is the location of the error. That error may be a content\n// error (invalid JSON) or an input error (e.g. network failure).\nDecodeJsonResult DecodeJson(DecodeJsonCallbacks&& callbacks,\n                   " +
+	"         sync_io::Input&& input,\n                            wuffs_base__slice_u32 quirks);\n\n}  // namespace wuffs_aux\n" +
 	""
 
 var AuxNonBaseCcFiles = []string{
diff --git a/release/c/wuffs-unsupported-snapshot.c b/release/c/wuffs-unsupported-snapshot.c
index 781b156..12b0edf 100644
--- a/release/c/wuffs-unsupported-snapshot.c
+++ b/release/c/wuffs-unsupported-snapshot.c
@@ -8459,6 +8459,8 @@
   //
   // Do not keep a reference to buffer or buffer.data.ptr after Done returns,
   // as DecodeCbor may then de-allocate the backing array.
+  //
+  // The default Done implementation is a no-op.
   virtual void Done(DecodeCborResult& result,
                     sync_io::Input& input,
                     IOBuffer& buffer);
@@ -8493,10 +8495,21 @@
   // strings, the Callbacks implementation is responsible for tracking map keys
   // versus other values.
 
+  // The JSON file format as specified deals only with (UTF-8) text strings,
+  // but an unofficial extension allows "ijk\x89m" escapes within those
+  // strings. DecodeJsonCallbacks' AppendByteString will not be called unless
+  // WUFFS_JSON__QUIRK_ALLOW_BACKSLASH_X_AS_BYTES is passed to DecodeJson. If
+  // it is passed, AppendTextString will not be called and all byte strings are
+  // potentially invalid UTF-8. It is up to the AppendByteString implementation
+  // whether to test the std::string for UTF-8 validity.
+  //
+  // The default AppendByteString implementation returns an error message.
+
   virtual std::string AppendNull() = 0;
   virtual std::string AppendBool(bool val) = 0;
   virtual std::string AppendF64(double val) = 0;
   virtual std::string AppendI64(int64_t val) = 0;
+  virtual std::string AppendByteString(std::string&& val);
   virtual std::string AppendTextString(std::string&& val) = 0;
 
   // Push and Pop are called for container nodes: JSON arrays (lists) and JSON
@@ -8522,6 +8535,8 @@
   //
   // Do not keep a reference to buffer or buffer.data.ptr after Done returns,
   // as DecodeJson may then de-allocate the backing array.
+  //
+  // The default Done implementation is a no-op.
   virtual void Done(DecodeJsonResult& result,
                     sync_io::Input& input,
                     IOBuffer& buffer);
@@ -28939,9 +28954,10 @@
     : error_message(std::move(error_message0)),
       cursor_position(cursor_position0) {}
 
-void DecodeCborCallbacks::Done(DecodeCborResult& result,
-                               sync_io::Input& input,
-                               IOBuffer& buffer) {}
+void  //
+DecodeCborCallbacks::Done(DecodeCborResult& result,
+                          sync_io::Input& input,
+                          IOBuffer& buffer) {}
 
 DecodeCborResult  //
 DecodeCbor(DecodeCborCallbacks&& callbacks,
@@ -29267,9 +29283,15 @@
     : error_message(std::move(error_message0)),
       cursor_position(cursor_position0) {}
 
-void DecodeJsonCallbacks::Done(DecodeJsonResult& result,
-                               sync_io::Input& input,
-                               IOBuffer& buffer) {}
+std::string  //
+DecodeJsonCallbacks::AppendByteString(std::string&& val) {
+  return "wuffs_aux::JsonDecoder: unexpected JSON byte string";
+}
+
+void  //
+DecodeJsonCallbacks::Done(DecodeJsonResult& result,
+                          sync_io::Input& input,
+                          IOBuffer& buffer) {}
 
 DecodeJsonResult  //
 DecodeJson(DecodeJsonCallbacks&& callbacks,
@@ -29398,13 +29420,43 @@
             const char* ptr =  // Convert from (uint8_t*).
                 static_cast<const char*>(static_cast<void*>(token_ptr));
             str.append(ptr, token_len);
+          } else if (
+              vbd &
+              WUFFS_BASE__TOKEN__VBD__STRING__CONVERT_1_DST_4_SRC_BACKSLASH_X) {
+            wuffs_base__slice_u8 encoded =
+                wuffs_base__make_slice_u8(token_ptr, token_len);
+            while (encoded.len > 0) {
+              uint8_t decoded[64];
+              constexpr bool src_closed = true;
+              wuffs_base__transform__output o = wuffs_base__base_16__decode4(
+                  wuffs_base__make_slice_u8(&decoded[0], sizeof decoded),
+                  encoded, src_closed, WUFFS_BASE__BASE_16__DEFAULT_OPTIONS);
+              if (o.status.is_error()) {
+                ret_error_message = o.status.message();
+                goto done;
+              } else if ((o.num_dst > (sizeof decoded)) ||
+                         (o.num_src > encoded.len)) {
+                ret_error_message =
+                    "wuffs_aux::JsonDecoder: internal error: inconsistent "
+                    "base16 decoding";
+                goto done;
+              }
+              str.append(  // Convert from (uint8_t*).
+                  static_cast<const char*>(static_cast<void*>(&decoded[0])),
+                  o.num_dst);
+              encoded.ptr += o.num_src;
+              encoded.len -= o.num_src;
+            }
           } else {
             goto fail;
           }
           if (token.continued()) {
             continue;
           }
-          ret_error_message = callbacks.AppendTextString(std::move(str));
+          ret_error_message =
+              (vbd & WUFFS_BASE__TOKEN__VBD__STRING__CHAIN_MUST_BE_UTF_8)
+                  ? callbacks.AppendTextString(std::move(str))
+                  : callbacks.AppendByteString(std::move(str));
           str.clear();
           goto parsed_a_value;
         }