"json" --- JSON encoder and decoder
***********************************

**Source code:** Lib/json/__init__.py

======================================================================

JSON (JavaScript Object Notation), specified by **RFC 7159** (which
obsoletes **RFC 4627**) and by ECMA-404, is a lightweight data
interchange format inspired by JavaScript object literal syntax
(although it is not a strict subset of JavaScript [1] ).

Note:

  The term "object" in the context of JSON processing in Python can be
  ambiguous. All values in Python are objects. In JSON, an object
  refers to any data wrapped in curly braces, similar to a Python
  dictionary.

Warning:

  Be cautious when parsing JSON data from untrusted sources. A
  malicious JSON string may cause the decoder to consume considerable
  CPU and memory resources. Limiting the size of data to be parsed is
  recommended.

This module exposes an API familiar to users of the standard library
"marshal" and "pickle" modules.

Encoding basic Python object hierarchies:

   >>> import json
   >>> json.dumps(['foo', {'bar': ('baz', None, 1.0, 2)}])
   '["foo", {"bar": ["baz", null, 1.0, 2]}]'
   >>> print(json.dumps("\"foo\bar"))
   "\"foo\bar"
   >>> print(json.dumps('\u1234'))
   "\u1234"
   >>> print(json.dumps('\\'))
   "\\"
   >>> print(json.dumps({"c": 0, "b": 0, "a": 0}, sort_keys=True))
   {"a": 0, "b": 0, "c": 0}
   >>> from io import StringIO
   >>> io = StringIO()
   >>> json.dump(['streaming API'], io)
   >>> io.getvalue()
   '["streaming API"]'

Compact encoding:

   >>> import json
   >>> json.dumps([1, 2, 3, {'4': 5, '6': 7}], separators=(',', ':'))
   '[1,2,3,{"4":5,"6":7}]'

Pretty printing:

   >>> import json
   >>> print(json.dumps({'6': 7, '4': 5}, sort_keys=True, indent=4))
   {
       "4": 5,
       "6": 7
   }

Customizing JSON object encoding:

   >>> import json
   >>> def custom_json(obj):
   ...     if isinstance(obj, complex):
   ...         return {'__complex__': True, 'real': obj.real, 'imag': obj.imag}
   ...     raise TypeError(f'Cannot serialize object of {type(obj)}')
   ...
   >>> json.dumps(1 + 2j, default=custom_json)
   '{"__complex__": true, "real": 1.0, "imag": 2.0}'

Decoding JSON:

   >>> import json
   >>> json.loads('["foo", {"bar":["baz", null, 1.0, 2]}]')
   ['foo', {'bar': ['baz', None, 1.0, 2]}]
   >>> json.loads('"\\"foo\\bar"')
   '"foo\x08ar'
   >>> from io import StringIO
   >>> io = StringIO('["streaming API"]')
   >>> json.load(io)
   ['streaming API']

Customizing JSON object decoding:

   >>> import json
   >>> def as_complex(dct):
   ...     if '__complex__' in dct:
   ...         return complex(dct['real'], dct['imag'])
   ...     return dct
   ...
   >>> json.loads('{"__complex__": true, "real": 1, "imag": 2}',
   ...     object_hook=as_complex)
   (1+2j)
   >>> import decimal
   >>> json.loads('1.1', parse_float=decimal.Decimal)
   Decimal('1.1')

Extending "JSONEncoder":

   >>> import json
   >>> class ComplexEncoder(json.JSONEncoder):
   ...     def default(self, obj):
   ...         if isinstance(obj, complex):
   ...             return [obj.real, obj.imag]
   ...         # Let the base class default method raise the TypeError
   ...         return super().default(obj)
   ...
   >>> json.dumps(2 + 1j, cls=ComplexEncoder)
   '[2.0, 1.0]'
   >>> ComplexEncoder().encode(2 + 1j)
   '[2.0, 1.0]'
   >>> list(ComplexEncoder().iterencode(2 + 1j))
   ['[2.0', ', 1.0', ']']

Using "json" from the shell to validate and pretty-print:

   $ echo '{"json":"obj"}' | python -m json
   {
       "json": "obj"
   }
   $ echo '{1.2:3.4}' | python -m json
   Expecting property name enclosed in double quotes: line 1 column 2 (char 1)

See Command-line interface for detailed documentation.

Note:

  JSON is a subset of YAML 1.2.  The JSON produced by this module's
  default settings (in particular, the default *separators* value) is
  also a subset of YAML 1.0 and 1.1.  This module can thus also be
  used as a YAML serializer.

Note:

  This module's encoders and decoders preserve input and output order
  by default.  Order is only lost if the underlying containers are
  unordered.


Basic Usage
===========

json.dump(obj, fp, *, skipkeys=False, ensure_ascii=True, check_circular=True, allow_nan=True, cls=None, indent=None, separators=None, default=None, sort_keys=False, **kw)

   Serialize *obj* as a JSON formatted stream to *fp* (a
   ".write()"-supporting *file-like object*) using this Python-to-JSON
   conversion table.

   Note:

     Unlike "pickle" and "marshal", JSON is not a framed protocol, so
     trying to serialize multiple objects with repeated calls to
     "dump()" using the same *fp* will result in an invalid JSON file.

   Parameters:
      * **obj** (*object*) -- The Python object to be serialized.

      * **fp** (*file-like object*) -- The file-like object *obj* will
        be serialized to. The "json" module always produces "str"
        objects, not "bytes" objects, therefore "fp.write()" must
        support "str" input.

      * **skipkeys** (*bool*) -- If "True", keys that are not of a
        basic type ("str", "int", "float", "bool", "None") will be
        skipped instead of raising a "TypeError". Default "False".

      * **ensure_ascii** (*bool*) -- If "True" (the default), the
        output is guaranteed to have all incoming non-ASCII and non-
        printable characters escaped. If "False", all characters will
        be outputted as-is, except for the characters that must be
        escaped: quotation mark, reverse solidus, and the control
        characters U+0000 through U+001F.

      * **check_circular** (*bool*) -- If "False", the circular
        reference check for container types is skipped and a circular
        reference will result in a "RecursionError" (or worse).
        Default "True".

      * **allow_nan** (*bool*) -- If "False", serialization of out-of-
        range "float" values ("nan", "inf", "-inf") will result in a
        "ValueError", in strict compliance with the JSON
        specification. If "True" (the default), their JavaScript
        equivalents ("NaN", "Infinity", "-Infinity") are used.

      * **cls** (a "JSONEncoder" subclass) -- If set, a custom JSON
        encoder with the "default()" method overridden, for
        serializing into custom datatypes. If "None" (the default),
        "JSONEncoder" is used.

      * **indent** (*int** | **str** | **None*) -- If a positive
        integer or string, JSON array elements and object members will
        be pretty-printed with that indent level. A positive integer
        indents that many spaces per level; a string (such as ""\t"")
        is used to indent each level. If zero, negative, or """" (the
        empty string), only newlines are inserted. If "None" (the
        default), no newlines are inserted.

      * **separators** (*tuple** | **None*) -- A two-tuple:
        "(item_separator, key_separator)". If "None" (the default),
        *separators* defaults to "(', ', ': ')" if *indent* is "None",
        and "(',', ': ')" otherwise. For the most compact JSON,
        specify "(',', ':')" to eliminate whitespace.

      * **default** (*callable* | None) -- A function that is called
        for objects that can't otherwise be serialized. It should
        return a JSON encodable version of the object or raise a
        "TypeError". If "None" (the default), "TypeError" is raised.

      * **sort_keys** (*bool*) -- If "True", dictionaries will be
        outputted sorted by key. Default "False".

   Changed in version 3.2: Allow strings for *indent* in addition to
   integers.

   Changed in version 3.4: Use "(',', ': ')" as default if *indent* is
   not "None".

   Changed in version 3.6: All optional parameters are now keyword-
   only.

json.dumps(obj, *, skipkeys=False, ensure_ascii=True, check_circular=True, allow_nan=True, cls=None, indent=None, separators=None, default=None, sort_keys=False, **kw)

   Serialize *obj* to a JSON formatted "str" using this conversion
   table.  The arguments have the same meaning as in "dump()".

   Note:

     Keys in key/value pairs of JSON are always of the type "str".
     When a dictionary is converted into JSON, all the keys of the
     dictionary are coerced to strings. As a result of this, if a
     dictionary is converted into JSON and then back into a
     dictionary, the dictionary may not equal the original one. That
     is, "loads(dumps(x)) != x" if x has non-string keys.

json.load(fp, *, cls=None, object_hook=None, parse_float=None, parse_int=None, parse_constant=None, object_pairs_hook=None, **kw)

   Deserialize *fp* to a Python object using the JSON-to-Python
   conversion table.

   Parameters:
      * **fp** (*file-like object*) -- A ".read()"-supporting *text
        file* or *binary file* containing the JSON document to be
        deserialized.

      * **cls** (a "JSONDecoder" subclass) -- If set, a custom JSON
        decoder. Additional keyword arguments to "load()" will be
        passed to the constructor of *cls*. If "None" (the default),
        "JSONDecoder" is used.

      * **object_hook** (*callable* | None) -- If set, a function that
        is called with the result of any JSON object literal decoded
        (a "dict"). The return value of this function will be used
        instead of the "dict". This feature can be used to implement
        custom decoders, for example JSON-RPC class hinting. Default
        "None".

      * **object_pairs_hook** (*callable* | None) -- If set, a
        function that is called with the result of any JSON object
        literal decoded with an ordered list of pairs. The return
        value of this function will be used instead of the "dict".
        This feature can be used to implement custom decoders. If
        *object_hook* is also set, *object_pairs_hook* takes priority.
        Default "None".

      * **parse_float** (*callable* | None) -- If set, a function that
        is called with the string of every JSON float to be decoded.
        If "None" (the default), it is equivalent to "float(num_str)".
        This can be used to parse JSON floats into custom datatypes,
        for example "decimal.Decimal".

      * **parse_int** (*callable* | None) -- If set, a function that
        is called with the string of every JSON int to be decoded. If
        "None" (the default), it is equivalent to "int(num_str)". This
        can be used to parse JSON integers into custom datatypes, for
        example "float".

      * **parse_constant** (*callable* | None) -- If set, a function
        that is called with one of the following strings:
        "'-Infinity'", "'Infinity'", or "'NaN'". This can be used to
        raise an exception if invalid JSON numbers are encountered.
        Default "None".

   Raises:
      * **JSONDecodeError** -- When the data being deserialized is not
        a valid JSON document.

      * **UnicodeDecodeError** -- When the data being deserialized
        does not contain UTF-8, UTF-16 or UTF-32 encoded data.

   Changed in version 3.1:

   * Added the optional *object_pairs_hook* parameter.

   * *parse_constant* doesn't get called on 'null', 'true', 'false'
     anymore.

   Changed in version 3.6:

   * All optional parameters are now keyword-only.

   * *fp* can now be a *binary file*. The input encoding should be
     UTF-8, UTF-16 or UTF-32.

   Changed in version 3.11: The default *parse_int* of "int()" now
   limits the maximum length of the integer string via the
   interpreter's integer string conversion length limitation to help
   avoid denial of service attacks.

json.loads(s, *, cls=None, object_hook=None, parse_float=None, parse_int=None, parse_constant=None, object_pairs_hook=None, **kw)

   Identical to "load()", but instead of a file-like object,
   deserialize *s* (a "str", "bytes" or "bytearray" instance
   containing a JSON document) to a Python object using this
   conversion table.

   Changed in version 3.6: *s* can now be of type "bytes" or
   "bytearray". The input encoding should be UTF-8, UTF-16 or UTF-32.

   Changed in version 3.9: The keyword argument *encoding* has been
   removed.


Encoders and Decoders
=====================

class json.JSONDecoder(*, object_hook=None, parse_float=None, parse_int=None, parse_constant=None, strict=True, object_pairs_hook=None)

   Simple JSON decoder.

   Performs the following translations in decoding by default:

   +-----------------+---------------------+
   | JSON            | Python              |
   |=================|=====================|
   | object          | dict                |
   +-----------------+---------------------+
   | array           | list                |
   +-----------------+---------------------+
   | string          | str                 |
   +-----------------+---------------------+
   | number (int)    | int                 |
   +-----------------+---------------------+
   | number (real)   | float               |
   +-----------------+---------------------+
   | true            | True                |
   +-----------------+---------------------+
   | false           | False               |
   +-----------------+---------------------+
   | null            | None                |
   +-----------------+---------------------+

   It also understands "NaN", "Infinity", and "-Infinity" as their
   corresponding "float" values, which is outside the JSON spec.

   *object_hook* is an optional function that will be called with the
   result of every JSON object decoded and its return value will be
   used in place of the given "dict".  This can be used to provide
   custom deserializations (e.g. to support JSON-RPC class hinting).

   *object_pairs_hook* is an optional function that will be called
   with the result of every JSON object decoded with an ordered list
   of pairs.  The return value of *object_pairs_hook* will be used
   instead of the "dict".  This feature can be used to implement
   custom decoders.  If *object_hook* is also defined, the
   *object_pairs_hook* takes priority.

   Changed in version 3.1: Added support for *object_pairs_hook*.

   *parse_float* is an optional function that will be called with the
   string of every JSON float to be decoded.  By default, this is
   equivalent to "float(num_str)".  This can be used to use another
   datatype or parser for JSON floats (e.g. "decimal.Decimal").

   *parse_int* is an optional function that will be called with the
   string of every JSON int to be decoded.  By default, this is
   equivalent to "int(num_str)".  This can be used to use another
   datatype or parser for JSON integers (e.g. "float").

   *parse_constant* is an optional function that will be called with
   one of the following strings: "'-Infinity'", "'Infinity'", "'NaN'".
   This can be used to raise an exception if invalid JSON numbers are
   encountered.

   If *strict* is false ("True" is the default), then control
   characters will be allowed inside strings.  Control characters in
   this context are those with character codes in the 0--31 range,
   including "'\t'" (tab), "'\n'", "'\r'" and "'\0'".

   If the data being deserialized is not a valid JSON document, a
   "JSONDecodeError" will be raised.

   Changed in version 3.6: All parameters are now keyword-only.

   decode(s)

      Return the Python representation of *s* (a "str" instance
      containing a JSON document).

      "JSONDecodeError" will be raised if the given JSON document is
      not valid.

   raw_decode(s)

      Decode a JSON document from *s* (a "str" beginning with a JSON
      document) and return a 2-tuple of the Python representation and
      the index in *s* where the document ended.

      This can be used to decode a JSON document from a string that
      may have extraneous data at the end.

class json.JSONEncoder(*, skipkeys=False, ensure_ascii=True, check_circular=True, allow_nan=True, sort_keys=False, indent=None, separators=None, default=None)

   Extensible JSON encoder for Python data structures.

   Supports the following objects and types by default:

   +------------------------------------------+-----------------+
   | Python                                   | JSON            |
   |==========================================|=================|
   | dict                                     | object          |
   +------------------------------------------+-----------------+
   | list, tuple                              | array           |
   +------------------------------------------+-----------------+
   | str                                      | string          |
   +------------------------------------------+-----------------+
   | int, float, int- & float-derived Enums   | number          |
   +------------------------------------------+-----------------+
   | True                                     | true            |
   +------------------------------------------+-----------------+
   | False                                    | false           |
   +------------------------------------------+-----------------+
   | None                                     | null            |
   +------------------------------------------+-----------------+

   Changed in version 3.4: Added support for int- and float-derived
   Enum classes.

   To extend this to recognize other objects, subclass and implement a
   "default()" method with another method that returns a serializable
   object for "o" if possible, otherwise it should call the superclass
   implementation (to raise "TypeError").

   If *skipkeys* is false (the default), a "TypeError" will be raised
   when trying to encode keys that are not "str", "int", "float",
   "bool" or "None".  If *skipkeys* is true, such items are simply
   skipped.

   If *ensure_ascii* is true (the default), the output is guaranteed
   to have all incoming non-ASCII and non-printable characters
   escaped. If *ensure_ascii* is false, all characters will be output
   as-is, except for the characters that must be escaped: quotation
   mark, reverse solidus, and the control characters U+0000 through
   U+001F.

   If *check_circular* is true (the default), then lists, dicts, and
   custom encoded objects will be checked for circular references
   during encoding to prevent an infinite recursion (which would cause
   a "RecursionError"). Otherwise, no such check takes place.

   If *allow_nan* is true (the default), then "NaN", "Infinity", and
   "-Infinity" will be encoded as such.  This behavior is not JSON
   specification compliant, but is consistent with most JavaScript
   based encoders and decoders.  Otherwise, it will be a "ValueError"
   to encode such floats.

   If *sort_keys* is true (default: "False"), then the output of
   dictionaries will be sorted by key; this is useful for regression
   tests to ensure that JSON serializations can be compared on a day-
   to-day basis.

   If *indent* is a non-negative integer or string, then JSON array
   elements and object members will be pretty-printed with that indent
   level.  An indent level of 0, negative, or """" will only insert
   newlines.  "None" (the default) selects the most compact
   representation. Using a positive integer indent indents that many
   spaces per level.  If *indent* is a string (such as ""\t""), that
   string is used to indent each level.

   Changed in version 3.2: Allow strings for *indent* in addition to
   integers.

   If specified, *separators* should be an "(item_separator,
   key_separator)" tuple.  The default is "(', ', ': ')" if *indent*
   is "None" and "(',', ': ')" otherwise.  To get the most compact
   JSON representation, you should specify "(',', ':')" to eliminate
   whitespace.

   Changed in version 3.4: Use "(',', ': ')" as default if *indent* is
   not "None".

   If specified, *default* should be a function that gets called for
   objects that can't otherwise be serialized.  It should return a
   JSON encodable version of the object or raise a "TypeError".  If
   not specified, "TypeError" is raised.

   Changed in version 3.6: All parameters are now keyword-only.

   default(o)

      Implement this method in a subclass such that it returns a
      serializable object for *o*, or calls the base implementation
      (to raise a "TypeError").

      For example, to support arbitrary iterators, you could implement
      "default()" like this:

         def default(self, o):
            try:
                iterable = iter(o)
            except TypeError:
                pass
            else:
                return list(iterable)
            # Let the base class default method raise the TypeError
            return super().default(o)

   encode(o)

      Return a JSON string representation of a Python data structure,
      *o*.  For example:

         >>> json.JSONEncoder().encode({"foo": ["bar", "baz"]})
         '{"foo": ["bar", "baz"]}'

   iterencode(o)

      Encode the given object, *o*, and yield each string
      representation as available.  For example:

         for chunk in json.JSONEncoder().iterencode(bigobject):
             mysocket.write(chunk)


Exceptions
==========

exception json.JSONDecodeError(msg, doc, pos)

   Subclass of "ValueError" with the following additional attributes:

   msg

      The unformatted error message.

   doc

      The JSON document being parsed.

   pos

      The start index of *doc* where parsing failed.

   lineno

      The line corresponding to *pos*.

   colno

      The column corresponding to *pos*.

   Added in version 3.5.


Standard Compliance and Interoperability
========================================

The JSON format is specified by **RFC 7159** and by ECMA-404. This
section details this module's level of compliance with the RFC. For
simplicity, "JSONEncoder" and "JSONDecoder" subclasses, and parameters
other than those explicitly mentioned, are not considered.

This module does not comply with the RFC in a strict fashion,
implementing some extensions that are valid JavaScript but not valid
JSON.  In particular:

* Infinite and NaN number values are accepted and output;

* Repeated names within an object are accepted, and only the value of
  the last name-value pair is used.

Since the RFC permits RFC-compliant parsers to accept input texts that
are not RFC-compliant, this module's deserializer is technically RFC-
compliant under default settings.


Character Encodings
-------------------

The RFC requires that JSON be represented using either UTF-8, UTF-16,
or UTF-32, with UTF-8 being the recommended default for maximum
interoperability.

As permitted, though not required, by the RFC, this module's
serializer sets *ensure_ascii=True* by default, thus escaping the
output so that the resulting strings only contain printable ASCII
characters.

Other than the *ensure_ascii* parameter, this module is defined
strictly in terms of conversion between Python objects and "Unicode
strings", and thus does not otherwise directly address the issue of
character encodings.

The RFC prohibits adding a byte order mark (BOM) to the start of a
JSON text, and this module's serializer does not add a BOM to its
output. The RFC permits, but does not require, JSON deserializers to
ignore an initial BOM in their input.  This module's deserializer
raises a "ValueError" when an initial BOM is present.

The RFC does not explicitly forbid JSON strings which contain byte
sequences that don't correspond to valid Unicode characters (e.g.
unpaired UTF-16 surrogates), but it does note that they may cause
interoperability problems. By default, this module accepts and outputs
(when present in the original "str") code points for such sequences.


Infinite and NaN Number Values
------------------------------

The RFC does not permit the representation of infinite or NaN number
values. Despite that, by default, this module accepts and outputs
"Infinity", "-Infinity", and "NaN" as if they were valid JSON number
literal values:

   >>> # Neither of these calls raises an exception, but the results are not valid JSON
   >>> json.dumps(float('-inf'))
   '-Infinity'
   >>> json.dumps(float('nan'))
   'NaN'
   >>> # Same when deserializing
   >>> json.loads('-Infinity')
   -inf
   >>> json.loads('NaN')
   nan

In the serializer, the *allow_nan* parameter can be used to alter this
behavior.  In the deserializer, the *parse_constant* parameter can be
used to alter this behavior.


Repeated Names Within an Object
-------------------------------

The RFC specifies that the names within a JSON object should be
unique, but does not mandate how repeated names in JSON objects should
be handled.  By default, this module does not raise an exception;
instead, it ignores all but the last name-value pair for a given name:

   >>> weird_json = '{"x": 1, "x": 2, "x": 3}'
   >>> json.loads(weird_json)
   {'x': 3}

The *object_pairs_hook* parameter can be used to alter this behavior.


Top-level Non-Object, Non-Array Values
--------------------------------------

The old version of JSON specified by the obsolete **RFC 4627**
required that the top-level value of a JSON text must be either a JSON
object or array (Python "dict" or "list"), and could not be a JSON
null, boolean, number, or string value.  **RFC 7159** removed that
restriction, and this module does not and has never implemented that
restriction in either its serializer or its deserializer.

Regardless, for maximum interoperability, you may wish to voluntarily
adhere to the restriction yourself.


Implementation Limitations
--------------------------

Some JSON deserializer implementations may set limits on:

* the size of accepted JSON texts

* the maximum level of nesting of JSON objects and arrays

* the range and precision of JSON numbers

* the content and maximum length of JSON strings

This module does not impose any such limits beyond those of the
relevant Python datatypes themselves or the Python interpreter itself.

When serializing to JSON, beware any such limitations in applications
that may consume your JSON.  In particular, it is common for JSON
numbers to be deserialized into IEEE 754 double precision numbers and
thus subject to that representation's range and precision limitations.
This is especially relevant when serializing Python "int" values of
extremely large magnitude, or when serializing instances of "exotic"
numerical types such as "decimal.Decimal".


Command-line interface
======================

**Source code:** Lib/json/tool.py

======================================================================

The "json" module can be invoked as a script via "python -m json" to
validate and pretty-print JSON objects. The "json.tool" submodule
implements this interface.

If the optional "infile" and "outfile" arguments are not specified,
"sys.stdin" and "sys.stdout" will be used respectively:

   $ echo '{"json": "obj"}' | python -m json
   {
       "json": "obj"
   }
   $ echo '{1.2:3.4}' | python -m json
   Expecting property name enclosed in double quotes: line 1 column 2 (char 1)

Changed in version 3.5: The output is now in the same order as the
input. Use the "--sort-keys" option to sort the output of dictionaries
alphabetically by key.

Changed in version 3.14: The "json" module may now be directly
executed as "python -m json". For backwards compatibility, invoking
the CLI as "python -m json.tool" remains supported.


Command-line options
--------------------

infile

   The JSON file to be validated or pretty-printed:

      $ python -m json mp_films.json
      [
          {
              "title": "And Now for Something Completely Different",
              "year": 1971
          },
          {
              "title": "Monty Python and the Holy Grail",
              "year": 1975
          }
      ]

   If *infile* is not specified, read from "sys.stdin".

outfile

   Write the output of the *infile* to the given *outfile*. Otherwise,
   write it to "sys.stdout".

--sort-keys

   Sort the output of dictionaries alphabetically by key.

   Added in version 3.5.

--no-ensure-ascii

   Disable escaping of non-ascii characters, see "json.dumps()" for
   more information.

   Added in version 3.9.

--json-lines

   Parse every input line as separate JSON object.

   Added in version 3.8.

--indent, --tab, --no-indent, --compact

   Mutually exclusive options for whitespace control.

   Added in version 3.9.

-h, --help

   Show the help message.

-[ Footnotes ]-

[1] As noted in the errata for RFC 7159, JSON permits literal U+2028
    (LINE SEPARATOR) and U+2029 (PARAGRAPH SEPARATOR) characters in
    strings, whereas JavaScript (as of ECMAScript Edition 5.1) does
    not.
