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[chromium-blink-merge.git] / third_party / JSON / JSON-2.59 / README

JSON version 2.58
=================

"JSON::PP" was earlier included in the "JSON" distribution,
but has since Perl 5.14 been a core module. For this reason,
"JSON::PP" was removed from the "JSON" distribution and can
now be found also in the Perl5 repository at

    http://perl5.git.perl.org/perl.git

(The newest "JSON::PP" version still exists in CPAN.)

Instead, the "JSON" distribution will include "JSON::backportPP"
for backwards computability. JSON.pm should thus work as it did before.

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

INSTALLATION

To install this module type the following:

   perl Makefile.PL
   make
   make test
   make install

if you use cpanm, can install JSON::XS at once.

   cpanm  --with-recommends JSON


NAME
    JSON - JSON (JavaScript Object Notation) encoder/decoder

SYNOPSIS
     use JSON; # imports encode_json, decode_json, to_json and from_json.
 
     # simple and fast interfaces (expect/generate UTF-8)
 
     $utf8_encoded_json_text = encode_json $perl_hash_or_arrayref;
     $perl_hash_or_arrayref  = decode_json $utf8_encoded_json_text;
 
     # OO-interface
 
     $json = JSON->new->allow_nonref;
 
     $json_text   = $json->encode( $perl_scalar );
     $perl_scalar = $json->decode( $json_text );
 
     $pretty_printed = $json->pretty->encode( $perl_scalar ); # pretty-printing
 
     # If you want to use PP only support features, call with '-support_by_pp'
     # When XS unsupported feature is enable, using PP (de|en)code instead of XS ones.
 
     use JSON -support_by_pp;
 
     # option-acceptable interfaces (expect/generate UNICODE by default)
 
     $json_text   = to_json( $perl_scalar, { ascii => 1, pretty => 1 } );
     $perl_scalar = from_json( $json_text, { utf8  => 1 } );
 
     # Between (en|de)code_json and (to|from)_json, if you want to write
     # a code which communicates to an outer world (encoded in UTF-8),
     # recommend to use (en|de)code_json.

VERSION
        2.58

    This version is compatible with JSON::XS 2.27 and later.

NOTE
    JSON::PP was earlier included in the "JSON" distribution, but has since
    Perl 5.14 been a core module. For this reason, JSON::PP was removed from
    the JSON distribution and can now be found also in the Perl5 repository
    at

    *   <http://perl5.git.perl.org/perl.git>

    (The newest JSON::PP version still exists in CPAN.)

    Instead, the "JSON" distribution will include JSON::backportPP for
    backwards computability. JSON.pm should thus work as it did before.

DESCRIPTION
     ************************** CAUTION ********************************
     * This is 'JSON module version 2' and there are many differences  *
     * to version 1.xx                                                 *
     * Please check your applications using old version.              *
     *   See to 'INCOMPATIBLE CHANGES TO OLD VERSION'                  *
     *******************************************************************

    JSON (JavaScript Object Notation) is a simple data format. See to
    <http://www.json.org/> and
    "RFC4627"(<http://www.ietf.org/rfc/rfc4627.txt>).

    This module converts Perl data structures to JSON and vice versa using
    either JSON::XS or JSON::PP.

    JSON::XS is the fastest and most proper JSON module on CPAN which must
    be compiled and installed in your environment. JSON::PP is a pure-Perl
    module which is bundled in this distribution and has a strong
    compatibility to JSON::XS.

    This module try to use JSON::XS by default and fail to it, use JSON::PP
    instead. So its features completely depend on JSON::XS or JSON::PP.

    See to "BACKEND MODULE DECISION".

    To distinguish the module name 'JSON' and the format type JSON, the
    former is quoted by C<> (its results vary with your using media), and
    the latter is left just as it is.

    Module name : "JSON"

    Format type : JSON

  FEATURES
    *   correct unicode handling

        This module (i.e. backend modules) knows how to handle Unicode,
        documents how and when it does so, and even documents what "correct"
        means.

        Even though there are limitations, this feature is available since
        Perl version 5.6.

        JSON::XS requires Perl 5.8.2 (but works correctly in 5.8.8 or
        later), so in older versions "JSON" should call JSON::PP as the
        backend which can be used since Perl 5.005.

        With Perl 5.8.x JSON::PP works, but from 5.8.0 to 5.8.2, because of
        a Perl side problem, JSON::PP works slower in the versions. And in
        5.005, the Unicode handling is not available. See to "UNICODE
        HANDLING ON PERLS" in JSON::PP for more information.

        See also to "A FEW NOTES ON UNICODE AND PERL" in JSON::XS and
        "ENCODING/CODESET_FLAG_NOTES" in JSON::XS.

    *   round-trip integrity

        When you serialise a perl data structure using only data types
        supported by JSON and Perl, the deserialised data structure is
        identical on the Perl level. (e.g. the string "2.0" doesn't suddenly
        become "2" just because it looks like a number). There *are* minor
        exceptions to this, read the "MAPPING" section below to learn about
        those.

    *   strict checking of JSON correctness

        There is no guessing, no generating of illegal JSON texts by
        default, and only JSON is accepted as input by default (the latter
        is a security feature).

        See to "FEATURES" in JSON::XS and "FEATURES" in JSON::PP.

    *   fast

        This module returns a JSON::XS object itself if available. Compared
        to other JSON modules and other serialisers such as Storable,
        JSON::XS usually compares favorably in terms of speed, too.

        If not available, "JSON" returns a JSON::PP object instead of
        JSON::XS and it is very slow as pure-Perl.

    *   simple to use

        This module has both a simple functional interface as well as an
        object oriented interface interface.

    *   reasonably versatile output formats

        You can choose between the most compact guaranteed-single-line
        format possible (nice for simple line-based protocols), a pure-ASCII
        format (for when your transport is not 8-bit clean, still supports
        the whole Unicode range), or a pretty-printed format (for when you
        want to read that stuff). Or you can combine those features in
        whatever way you like.

FUNCTIONAL INTERFACE
    Some documents are copied and modified from "FUNCTIONAL INTERFACE" in
    JSON::XS. "to_json" and "from_json" are additional functions.

  encode_json
        $json_text = encode_json $perl_scalar

    Converts the given Perl data structure to a UTF-8 encoded, binary
    string.

    This function call is functionally identical to:

        $json_text = JSON->new->utf8->encode($perl_scalar)

  decode_json
        $perl_scalar = decode_json $json_text

    The opposite of "encode_json": expects an UTF-8 (binary) string and
    tries to parse that as an UTF-8 encoded JSON text, returning the
    resulting reference.

    This function call is functionally identical to:

        $perl_scalar = JSON->new->utf8->decode($json_text)

  to_json
       $json_text = to_json($perl_scalar)

    Converts the given Perl data structure to a json string.

    This function call is functionally identical to:

       $json_text = JSON->new->encode($perl_scalar)

    Takes a hash reference as the second.

       $json_text = to_json($perl_scalar, $flag_hashref)

    So,

       $json_text = to_json($perl_scalar, {utf8 => 1, pretty => 1})

    equivalent to:

       $json_text = JSON->new->utf8(1)->pretty(1)->encode($perl_scalar)

    If you want to write a modern perl code which communicates to outer
    world, you should use "encode_json" (supposed that JSON data are encoded
    in UTF-8).

  from_json
       $perl_scalar = from_json($json_text)

    The opposite of "to_json": expects a json string and tries to parse it,
    returning the resulting reference.

    This function call is functionally identical to:

        $perl_scalar = JSON->decode($json_text)

    Takes a hash reference as the second.

        $perl_scalar = from_json($json_text, $flag_hashref)

    So,

        $perl_scalar = from_json($json_text, {utf8 => 1})

    equivalent to:

        $perl_scalar = JSON->new->utf8(1)->decode($json_text)

    If you want to write a modern perl code which communicates to outer
    world, you should use "decode_json" (supposed that JSON data are encoded
    in UTF-8).

  JSON::is_bool
        $is_boolean = JSON::is_bool($scalar)

    Returns true if the passed scalar represents either JSON::true or
    JSON::false, two constants that act like 1 and 0 respectively and are
    also used to represent JSON "true" and "false" in Perl strings.

  JSON::true
    Returns JSON true value which is blessed object. It "isa" JSON::Boolean
    object.

  JSON::false
    Returns JSON false value which is blessed object. It "isa" JSON::Boolean
    object.

  JSON::null
    Returns "undef".

    See MAPPING, below, for more information on how JSON values are mapped
    to Perl.

HOW DO I DECODE A DATA FROM OUTER AND ENCODE TO OUTER
    This section supposes that your perl version is 5.8 or later.

    If you know a JSON text from an outer world - a network, a file content,
    and so on, is encoded in UTF-8, you should use "decode_json" or "JSON"
    module object with "utf8" enable. And the decoded result will contain
    UNICODE characters.

      # from network
      my $json        = JSON->new->utf8;
      my $json_text   = CGI->new->param( 'json_data' );
      my $perl_scalar = $json->decode( $json_text );
  
      # from file content
      local $/;
      open( my $fh, '<', 'json.data' );
      $json_text   = <$fh>;
      $perl_scalar = decode_json( $json_text );

    If an outer data is not encoded in UTF-8, firstly you should "decode"
    it.

      use Encode;
      local $/;
      open( my $fh, '<', 'json.data' );
      my $encoding = 'cp932';
      my $unicode_json_text = decode( $encoding, <$fh> ); # UNICODE
  
      # or you can write the below code.
      #
      # open( my $fh, "<:encoding($encoding)", 'json.data' );
      # $unicode_json_text = <$fh>;

    In this case, $unicode_json_text is of course UNICODE string. So you
    cannot use "decode_json" nor "JSON" module object with "utf8" enable.
    Instead of them, you use "JSON" module object with "utf8" disable or
    "from_json".

      $perl_scalar = $json->utf8(0)->decode( $unicode_json_text );
      # or
      $perl_scalar = from_json( $unicode_json_text );

    Or "encode 'utf8'" and "decode_json":

      $perl_scalar = decode_json( encode( 'utf8', $unicode_json_text ) );
      # this way is not efficient.

    And now, you want to convert your $perl_scalar into JSON data and send
    it to an outer world - a network or a file content, and so on.

    Your data usually contains UNICODE strings and you want the converted
    data to be encoded in UTF-8, you should use "encode_json" or "JSON"
    module object with "utf8" enable.

      print encode_json( $perl_scalar ); # to a network? file? or display?
      # or
      print $json->utf8->encode( $perl_scalar );

    If $perl_scalar does not contain UNICODE but $encoding-encoded strings
    for some reason, then its characters are regarded as latin1 for perl
    (because it does not concern with your $encoding). You cannot use
    "encode_json" nor "JSON" module object with "utf8" enable. Instead of
    them, you use "JSON" module object with "utf8" disable or "to_json".
    Note that the resulted text is a UNICODE string but no problem to print
    it.

      # $perl_scalar contains $encoding encoded string values
      $unicode_json_text = $json->utf8(0)->encode( $perl_scalar );
      # or 
      $unicode_json_text = to_json( $perl_scalar );
      # $unicode_json_text consists of characters less than 0x100
      print $unicode_json_text;

    Or "decode $encoding" all string values and "encode_json":

      $perl_scalar->{ foo } = decode( $encoding, $perl_scalar->{ foo } );
      # ... do it to each string values, then encode_json
      $json_text = encode_json( $perl_scalar );

    This method is a proper way but probably not efficient.

    See to Encode, perluniintro.

COMMON OBJECT-ORIENTED INTERFACE
  new
        $json = JSON->new

    Returns a new "JSON" object inherited from either JSON::XS or JSON::PP
    that can be used to de/encode JSON strings.

    All boolean flags described below are by default *disabled*.

    The mutators for flags all return the JSON object again and thus calls
    can be chained:

       my $json = JSON->new->utf8->space_after->encode({a => [1,2]})
       => {"a": [1, 2]}

  ascii
        $json = $json->ascii([$enable])
    
        $enabled = $json->get_ascii

    If $enable is true (or missing), then the encode method will not
    generate characters outside the code range 0..127. Any Unicode
    characters outside that range will be escaped using either a single
    \uXXXX or a double \uHHHH\uLLLLL escape sequence, as per RFC4627.

    If $enable is false, then the encode method will not escape Unicode
    characters unless required by the JSON syntax or other flags. This
    results in a faster and more compact format.

    This feature depends on the used Perl version and environment.

    See to "UNICODE HANDLING ON PERLS" in JSON::PP if the backend is PP.

      JSON->new->ascii(1)->encode([chr 0x10401])
      => ["\ud801\udc01"]

  latin1
        $json = $json->latin1([$enable])
    
        $enabled = $json->get_latin1

    If $enable is true (or missing), then the encode method will encode the
    resulting JSON text as latin1 (or iso-8859-1), escaping any characters
    outside the code range 0..255.

    If $enable is false, then the encode method will not escape Unicode
    characters unless required by the JSON syntax or other flags.

      JSON->new->latin1->encode (["\x{89}\x{abc}"]
      => ["\x{89}\\u0abc"]    # (perl syntax, U+abc escaped, U+89 not)

  utf8
        $json = $json->utf8([$enable])
    
        $enabled = $json->get_utf8

    If $enable is true (or missing), then the encode method will encode the
    JSON result into UTF-8, as required by many protocols, while the decode
    method expects to be handled an UTF-8-encoded string. Please note that
    UTF-8-encoded strings do not contain any characters outside the range
    0..255, they are thus useful for bytewise/binary I/O.

    In future versions, enabling this option might enable autodetection of
    the UTF-16 and UTF-32 encoding families, as described in RFC4627.

    If $enable is false, then the encode method will return the JSON string
    as a (non-encoded) Unicode string, while decode expects thus a Unicode
    string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs to be
    done yourself, e.g. using the Encode module.

    Example, output UTF-16BE-encoded JSON:

      use Encode;
      $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);

    Example, decode UTF-32LE-encoded JSON:

      use Encode;
      $object = JSON::XS->new->decode (decode "UTF-32LE", $jsontext);

    See to "UNICODE HANDLING ON PERLS" in JSON::PP if the backend is PP.

  pretty
        $json = $json->pretty([$enable])

    This enables (or disables) all of the "indent", "space_before" and
    "space_after" (and in the future possibly more) flags in one call to
    generate the most readable (or most compact) form possible.

    Equivalent to:

       $json->indent->space_before->space_after

    The indent space length is three and JSON::XS cannot change the indent
    space length.

  indent
        $json = $json->indent([$enable])
    
        $enabled = $json->get_indent

    If $enable is true (or missing), then the "encode" method will use a
    multiline format as output, putting every array member or object/hash
    key-value pair into its own line, identifying them properly.

    If $enable is false, no newlines or indenting will be produced, and the
    resulting JSON text is guaranteed not to contain any "newlines".

    This setting has no effect when decoding JSON texts.

    The indent space length is three. With JSON::PP, you can also access
    "indent_length" to change indent space length.

  space_before
        $json = $json->space_before([$enable])
    
        $enabled = $json->get_space_before

    If $enable is true (or missing), then the "encode" method will add an
    extra optional space before the ":" separating keys from values in JSON
    objects.

    If $enable is false, then the "encode" method will not add any extra
    space at those places.

    This setting has no effect when decoding JSON texts.

    Example, space_before enabled, space_after and indent disabled:

       {"key" :"value"}

  space_after
        $json = $json->space_after([$enable])
    
        $enabled = $json->get_space_after

    If $enable is true (or missing), then the "encode" method will add an
    extra optional space after the ":" separating keys from values in JSON
    objects and extra whitespace after the "," separating key-value pairs
    and array members.

    If $enable is false, then the "encode" method will not add any extra
    space at those places.

    This setting has no effect when decoding JSON texts.

    Example, space_before and indent disabled, space_after enabled:

       {"key": "value"}

  relaxed
        $json = $json->relaxed([$enable])
    
        $enabled = $json->get_relaxed

    If $enable is true (or missing), then "decode" will accept some
    extensions to normal JSON syntax (see below). "encode" will not be
    affected in anyway. *Be aware that this option makes you accept invalid
    JSON texts as if they were valid!*. I suggest only to use this option to
    parse application-specific files written by humans (configuration files,
    resource files etc.)

    If $enable is false (the default), then "decode" will only accept valid
    JSON texts.

    Currently accepted extensions are:

    *   list items can have an end-comma

        JSON *separates* array elements and key-value pairs with commas.
        This can be annoying if you write JSON texts manually and want to be
        able to quickly append elements, so this extension accepts comma at
        the end of such items not just between them:

           [
              1,
              2, <- this comma not normally allowed
           ]
           {
              "k1": "v1",
              "k2": "v2", <- this comma not normally allowed
           }

    *   shell-style '#'-comments

        Whenever JSON allows whitespace, shell-style comments are
        additionally allowed. They are terminated by the first
        carriage-return or line-feed character, after which more white-space
        and comments are allowed.

          [
             1, # this comment not allowed in JSON
                # neither this one...
          ]

  canonical
        $json = $json->canonical([$enable])
    
        $enabled = $json->get_canonical

    If $enable is true (or missing), then the "encode" method will output
    JSON objects by sorting their keys. This is adding a comparatively high
    overhead.

    If $enable is false, then the "encode" method will output key-value
    pairs in the order Perl stores them (which will likely change between
    runs of the same script).

    This option is useful if you want the same data structure to be encoded
    as the same JSON text (given the same overall settings). If it is
    disabled, the same hash might be encoded differently even if contains
    the same data, as key-value pairs have no inherent ordering in Perl.

    This setting has no effect when decoding JSON texts.

  allow_nonref
        $json = $json->allow_nonref([$enable])
    
        $enabled = $json->get_allow_nonref

    If $enable is true (or missing), then the "encode" method can convert a
    non-reference into its corresponding string, number or null JSON value,
    which is an extension to RFC4627. Likewise, "decode" will accept those
    JSON values instead of croaking.

    If $enable is false, then the "encode" method will croak if it isn't
    passed an arrayref or hashref, as JSON texts must either be an object or
    array. Likewise, "decode" will croak if given something that is not a
    JSON object or array.

       JSON->new->allow_nonref->encode ("Hello, World!")
       => "Hello, World!"

  allow_unknown
        $json = $json->allow_unknown ([$enable])
    
        $enabled = $json->get_allow_unknown

    If $enable is true (or missing), then "encode" will *not* throw an
    exception when it encounters values it cannot represent in JSON (for
    example, filehandles) but instead will encode a JSON "null" value. Note
    that blessed objects are not included here and are handled separately by
    c<allow_nonref>.

    If $enable is false (the default), then "encode" will throw an exception
    when it encounters anything it cannot encode as JSON.

    This option does not affect "decode" in any way, and it is recommended
    to leave it off unless you know your communications partner.

  allow_blessed
        $json = $json->allow_blessed([$enable])
    
        $enabled = $json->get_allow_blessed

    If $enable is true (or missing), then the "encode" method will not barf
    when it encounters a blessed reference. Instead, the value of the
    convert_blessed option will decide whether "null" ("convert_blessed"
    disabled or no "TO_JSON" method found) or a representation of the object
    ("convert_blessed" enabled and "TO_JSON" method found) is being encoded.
    Has no effect on "decode".

    If $enable is false (the default), then "encode" will throw an exception
    when it encounters a blessed object.

  convert_blessed
        $json = $json->convert_blessed([$enable])
    
        $enabled = $json->get_convert_blessed

    If $enable is true (or missing), then "encode", upon encountering a
    blessed object, will check for the availability of the "TO_JSON" method
    on the object's class. If found, it will be called in scalar context and
    the resulting scalar will be encoded instead of the object. If no
    "TO_JSON" method is found, the value of "allow_blessed" will decide what
    to do.

    The "TO_JSON" method may safely call die if it wants. If "TO_JSON"
    returns other blessed objects, those will be handled in the same way.
    "TO_JSON" must take care of not causing an endless recursion cycle (==
    crash) in this case. The name of "TO_JSON" was chosen because other
    methods called by the Perl core (== not by the user of the object) are
    usually in upper case letters and to avoid collisions with the "to_json"
    function or method.

    This setting does not yet influence "decode" in any way.

    If $enable is false, then the "allow_blessed" setting will decide what
    to do when a blessed object is found.

    convert_blessed_universally mode
        If use "JSON" with "-convert_blessed_universally", the
        "UNIVERSAL::TO_JSON" subroutine is defined as the below code:

           *UNIVERSAL::TO_JSON = sub {
               my $b_obj = B::svref_2object( $_[0] );
               return    $b_obj->isa('B::HV') ? { %{ $_[0] } }
                       : $b_obj->isa('B::AV') ? [ @{ $_[0] } ]
                       : undef
                       ;
           }

        This will cause that "encode" method converts simple blessed objects
        into JSON objects as non-blessed object.

           JSON -convert_blessed_universally;
           $json->allow_blessed->convert_blessed->encode( $blessed_object )

        This feature is experimental and may be removed in the future.

  filter_json_object
        $json = $json->filter_json_object([$coderef])

    When $coderef is specified, it will be called from "decode" each time it
    decodes a JSON object. The only argument passed to the coderef is a
    reference to the newly-created hash. If the code references returns a
    single scalar (which need not be a reference), this value (i.e. a copy
    of that scalar to avoid aliasing) is inserted into the deserialised data
    structure. If it returns an empty list (NOTE: *not* "undef", which is a
    valid scalar), the original deserialised hash will be inserted. This
    setting can slow down decoding considerably.

    When $coderef is omitted or undefined, any existing callback will be
    removed and "decode" will not change the deserialised hash in any way.

    Example, convert all JSON objects into the integer 5:

       my $js = JSON->new->filter_json_object (sub { 5 });
       # returns [5]
       $js->decode ('[{}]'); # the given subroutine takes a hash reference.
       # throw an exception because allow_nonref is not enabled
       # so a lone 5 is not allowed.
       $js->decode ('{"a":1, "b":2}');

  filter_json_single_key_object
        $json = $json->filter_json_single_key_object($key [=> $coderef])

    Works remotely similar to "filter_json_object", but is only called for
    JSON objects having a single key named $key.

    This $coderef is called before the one specified via
    "filter_json_object", if any. It gets passed the single value in the
    JSON object. If it returns a single value, it will be inserted into the
    data structure. If it returns nothing (not even "undef" but the empty
    list), the callback from "filter_json_object" will be called next, as if
    no single-key callback were specified.

    If $coderef is omitted or undefined, the corresponding callback will be
    disabled. There can only ever be one callback for a given key.

    As this callback gets called less often then the "filter_json_object"
    one, decoding speed will not usually suffer as much. Therefore,
    single-key objects make excellent targets to serialise Perl objects
    into, especially as single-key JSON objects are as close to the
    type-tagged value concept as JSON gets (it's basically an ID/VALUE
    tuple). Of course, JSON does not support this in any way, so you need to
    make sure your data never looks like a serialised Perl hash.

    Typical names for the single object key are "__class_whatever__", or
    "$__dollars_are_rarely_used__$" or "}ugly_brace_placement", or even
    things like "__class_md5sum(classname)__", to reduce the risk of
    clashing with real hashes.

    Example, decode JSON objects of the form "{ "__widget__" => <id> }" into
    the corresponding $WIDGET{<id>} object:

       # return whatever is in $WIDGET{5}:
       JSON
          ->new
          ->filter_json_single_key_object (__widget__ => sub {
                $WIDGET{ $_[0] }
             })
          ->decode ('{"__widget__": 5')

       # this can be used with a TO_JSON method in some "widget" class
       # for serialisation to json:
       sub WidgetBase::TO_JSON {
          my ($self) = @_;

          unless ($self->{id}) {
             $self->{id} = ..get..some..id..;
             $WIDGET{$self->{id}} = $self;
          }

          { __widget__ => $self->{id} }
       }

  shrink
        $json = $json->shrink([$enable])
    
        $enabled = $json->get_shrink

    With JSON::XS, this flag resizes strings generated by either "encode" or
    "decode" to their minimum size possible. This can save memory when your
    JSON texts are either very very long or you have many short strings. It
    will also try to downgrade any strings to octet-form if possible: perl
    stores strings internally either in an encoding called UTF-X or in
    octet-form. The latter cannot store everything but uses less space in
    general (and some buggy Perl or C code might even rely on that internal
    representation being used).

    With JSON::PP, it is noop about resizing strings but tries
    "utf8::downgrade" to the returned string by "encode". See to utf8.

    See to "OBJECT-ORIENTED INTERFACE" in JSON::XS and "METHODS" in
    JSON::PP.

  max_depth
        $json = $json->max_depth([$maximum_nesting_depth])
    
        $max_depth = $json->get_max_depth

    Sets the maximum nesting level (default 512) accepted while encoding or
    decoding. If a higher nesting level is detected in JSON text or a Perl
    data structure, then the encoder and decoder will stop and croak at that
    point.

    Nesting level is defined by number of hash- or arrayrefs that the
    encoder needs to traverse to reach a given point or the number of "{" or
    "[" characters without their matching closing parenthesis crossed to
    reach a given character in a string.

    If no argument is given, the highest possible setting will be used,
    which is rarely useful.

    Note that nesting is implemented by recursion in C. The default value
    has been chosen to be as large as typical operating systems allow
    without crashing. (JSON::XS)

    With JSON::PP as the backend, when a large value (100 or more) was set
    and it de/encodes a deep nested object/text, it may raise a warning
    'Deep recursion on subroutine' at the perl runtime phase.

    See "SECURITY CONSIDERATIONS" in JSON::XS for more info on why this is
    useful.

  max_size
        $json = $json->max_size([$maximum_string_size])
    
        $max_size = $json->get_max_size

    Set the maximum length a JSON text may have (in bytes) where decoding is
    being attempted. The default is 0, meaning no limit. When "decode" is
    called on a string that is longer then this many bytes, it will not
    attempt to decode the string but throw an exception. This setting has no
    effect on "encode" (yet).

    If no argument is given, the limit check will be deactivated (same as
    when 0 is specified).

    See "SECURITY CONSIDERATIONS" in JSON::XS, below, for more info on why
    this is useful.

  encode
        $json_text = $json->encode($perl_scalar)

    Converts the given Perl data structure (a simple scalar or a reference
    to a hash or array) to its JSON representation. Simple scalars will be
    converted into JSON string or number sequences, while references to
    arrays become JSON arrays and references to hashes become JSON objects.
    Undefined Perl values (e.g. "undef") become JSON "null" values.
    References to the integers 0 and 1 are converted into "true" and
    "false".

  decode
        $perl_scalar = $json->decode($json_text)

    The opposite of "encode": expects a JSON text and tries to parse it,
    returning the resulting simple scalar or reference. Croaks on error.

    JSON numbers and strings become simple Perl scalars. JSON arrays become
    Perl arrayrefs and JSON objects become Perl hashrefs. "true" becomes 1
    ("JSON::true"), "false" becomes 0 ("JSON::false") and "null" becomes
    "undef".

  decode_prefix
        ($perl_scalar, $characters) = $json->decode_prefix($json_text)

    This works like the "decode" method, but instead of raising an exception
    when there is trailing garbage after the first JSON object, it will
    silently stop parsing there and return the number of characters consumed
    so far.

       JSON->new->decode_prefix ("[1] the tail")
       => ([], 3)

    See to "OBJECT-ORIENTED INTERFACE" in JSON::XS

  property
        $boolean = $json->property($property_name)

    Returns a boolean value about above some properties.

    The available properties are "ascii", "latin1", "utf8",
    "indent","space_before", "space_after", "relaxed", "canonical",
    "allow_nonref", "allow_unknown", "allow_blessed", "convert_blessed",
    "shrink", "max_depth" and "max_size".

       $boolean = $json->property('utf8');
        => 0
       $json->utf8;
       $boolean = $json->property('utf8');
        => 1

    Sets the property with a given boolean value.

        $json = $json->property($property_name => $boolean);

    With no argument, it returns all the above properties as a hash
    reference.

        $flag_hashref = $json->property();

INCREMENTAL PARSING
    Most of this section are copied and modified from "INCREMENTAL PARSING"
    in JSON::XS.

    In some cases, there is the need for incremental parsing of JSON texts.
    This module does allow you to parse a JSON stream incrementally. It does
    so by accumulating text until it has a full JSON object, which it then
    can decode. This process is similar to using "decode_prefix" to see if a
    full JSON object is available, but is much more efficient (and can be
    implemented with a minimum of method calls).

    The backend module will only attempt to parse the JSON text once it is
    sure it has enough text to get a decisive result, using a very simple
    but truly incremental parser. This means that it sometimes won't stop as
    early as the full parser, for example, it doesn't detect parenthesis
    mismatches. The only thing it guarantees is that it starts decoding as
    soon as a syntactically valid JSON text has been seen. This means you
    need to set resource limits (e.g. "max_size") to ensure the parser will
    stop parsing in the presence if syntax errors.

    The following methods implement this incremental parser.

  incr_parse
        $json->incr_parse( [$string] ) # void context
    
        $obj_or_undef = $json->incr_parse( [$string] ) # scalar context
    
        @obj_or_empty = $json->incr_parse( [$string] ) # list context

    This is the central parsing function. It can both append new text and
    extract objects from the stream accumulated so far (both of these
    functions are optional).

    If $string is given, then this string is appended to the already
    existing JSON fragment stored in the $json object.

    After that, if the function is called in void context, it will simply
    return without doing anything further. This can be used to add more text
    in as many chunks as you want.

    If the method is called in scalar context, then it will try to extract
    exactly *one* JSON object. If that is successful, it will return this
    object, otherwise it will return "undef". If there is a parse error,
    this method will croak just as "decode" would do (one can then use
    "incr_skip" to skip the erroneous part). This is the most common way of
    using the method.

    And finally, in list context, it will try to extract as many objects
    from the stream as it can find and return them, or the empty list
    otherwise. For this to work, there must be no separators between the
    JSON objects or arrays, instead they must be concatenated back-to-back.
    If an error occurs, an exception will be raised as in the scalar context
    case. Note that in this case, any previously-parsed JSON texts will be
    lost.

    Example: Parse some JSON arrays/objects in a given string and return
    them.

        my @objs = JSON->new->incr_parse ("[5][7][1,2]");

  incr_text
        $lvalue_string = $json->incr_text

    This method returns the currently stored JSON fragment as an lvalue,
    that is, you can manipulate it. This *only* works when a preceding call
    to "incr_parse" in *scalar context* successfully returned an object.
    Under all other circumstances you must not call this function (I mean
    it. although in simple tests it might actually work, it *will* fail
    under real world conditions). As a special exception, you can also call
    this method before having parsed anything.

    This function is useful in two cases: a) finding the trailing text after
    a JSON object or b) parsing multiple JSON objects separated by non-JSON
    text (such as commas).

        $json->incr_text =~ s/\s*,\s*//;

    In Perl 5.005, "lvalue" attribute is not available. You must write codes
    like the below:

        $string = $json->incr_text;
        $string =~ s/\s*,\s*//;
        $json->incr_text( $string );

  incr_skip
        $json->incr_skip

    This will reset the state of the incremental parser and will remove the
    parsed text from the input buffer. This is useful after "incr_parse"
    died, in which case the input buffer and incremental parser state is
    left unchanged, to skip the text parsed so far and to reset the parse
    state.

  incr_reset
        $json->incr_reset

    This completely resets the incremental parser, that is, after this call,
    it will be as if the parser had never parsed anything.

    This is useful if you want to repeatedly parse JSON objects and want to
    ignore any trailing data, which means you have to reset the parser after
    each successful decode.

    See to "INCREMENTAL PARSING" in JSON::XS for examples.

JSON::PP SUPPORT METHODS
    The below methods are JSON::PP own methods, so when "JSON" works with
    JSON::PP (i.e. the created object is a JSON::PP object), available. See
    to "JSON::PP OWN METHODS" in JSON::PP in detail.

    If you use "JSON" with additional "-support_by_pp", some methods are
    available even with JSON::XS. See to "USE PP FEATURES EVEN THOUGH XS
    BACKEND".

       BEING { $ENV{PERL_JSON_BACKEND} = 'JSON::XS' }
   
       use JSON -support_by_pp;
   
       my $json = JSON->new;
       $json->allow_nonref->escape_slash->encode("/");

       # functional interfaces too.
       print to_json(["/"], {escape_slash => 1});
       print from_json('["foo"]', {utf8 => 1});

    If you do not want to all functions but "-support_by_pp", use
    "-no_export".

       use JSON -support_by_pp, -no_export;
       # functional interfaces are not exported.

  allow_singlequote
        $json = $json->allow_singlequote([$enable])

    If $enable is true (or missing), then "decode" will accept any JSON
    strings quoted by single quotations that are invalid JSON format.

        $json->allow_singlequote->decode({"foo":'bar'});
        $json->allow_singlequote->decode({'foo':"bar"});
        $json->allow_singlequote->decode({'foo':'bar'});

    As same as the "relaxed" option, this option may be used to parse
    application-specific files written by humans.

  allow_barekey
        $json = $json->allow_barekey([$enable])

    If $enable is true (or missing), then "decode" will accept bare keys of
    JSON object that are invalid JSON format.

    As same as the "relaxed" option, this option may be used to parse
    application-specific files written by humans.

        $json->allow_barekey->decode('{foo:"bar"}');

  allow_bignum
        $json = $json->allow_bignum([$enable])

    If $enable is true (or missing), then "decode" will convert the big
    integer Perl cannot handle as integer into a Math::BigInt object and
    convert a floating number (any) into a Math::BigFloat.

    On the contrary, "encode" converts "Math::BigInt" objects and
    "Math::BigFloat" objects into JSON numbers with "allow_blessed" enable.

       $json->allow_nonref->allow_blessed->allow_bignum;
       $bigfloat = $json->decode('2.000000000000000000000000001');
       print $json->encode($bigfloat);
       # => 2.000000000000000000000000001

    See to MAPPING about the conversion of JSON number.

  loose
        $json = $json->loose([$enable])

    The unescaped [\x00-\x1f\x22\x2f\x5c] strings are invalid in JSON
    strings and the module doesn't allow to "decode" to these (except for
    \x2f). If $enable is true (or missing), then "decode" will accept these
    unescaped strings.

        $json->loose->decode(qq|["abc
                                       def"]|);

    See to "JSON::PP OWN METHODS" in JSON::PP.

  escape_slash
        $json = $json->escape_slash([$enable])

    According to JSON Grammar, *slash* (U+002F) is escaped. But by default
    JSON backend modules encode strings without escaping slash.

    If $enable is true (or missing), then "encode" will escape slashes.

  indent_length
        $json = $json->indent_length($length)

    With JSON::XS, The indent space length is 3 and cannot be changed. With
    JSON::PP, it sets the indent space length with the given $length. The
    default is 3. The acceptable range is 0 to 15.

  sort_by
        $json = $json->sort_by($function_name)
        $json = $json->sort_by($subroutine_ref)

    If $function_name or $subroutine_ref are set, its sort routine are used.

       $js = $pc->sort_by(sub { $JSON::PP::a cmp $JSON::PP::b })->encode($obj);
       # is($js, q|{"a":1,"b":2,"c":3,"d":4,"e":5,"f":6,"g":7,"h":8,"i":9}|);

       $js = $pc->sort_by('own_sort')->encode($obj);
       # is($js, q|{"a":1,"b":2,"c":3,"d":4,"e":5,"f":6,"g":7,"h":8,"i":9}|);

       sub JSON::PP::own_sort { $JSON::PP::a cmp $JSON::PP::b }

    As the sorting routine runs in the JSON::PP scope, the given subroutine
    name and the special variables $a, $b will begin with 'JSON::PP::'.

    If $integer is set, then the effect is same as "canonical" on.

    See to "JSON::PP OWN METHODS" in JSON::PP.

MAPPING
    This section is copied from JSON::XS and modified to "JSON". JSON::XS
    and JSON::PP mapping mechanisms are almost equivalent.

    See to "MAPPING" in JSON::XS.

  JSON -> PERL
    object
        A JSON object becomes a reference to a hash in Perl. No ordering of
        object keys is preserved (JSON does not preserver object key
        ordering itself).

    array
        A JSON array becomes a reference to an array in Perl.

    string
        A JSON string becomes a string scalar in Perl - Unicode codepoints
        in JSON are represented by the same codepoints in the Perl string,
        so no manual decoding is necessary.

    number
        A JSON number becomes either an integer, numeric (floating point) or
        string scalar in perl, depending on its range and any fractional
        parts. On the Perl level, there is no difference between those as
        Perl handles all the conversion details, but an integer may take
        slightly less memory and might represent more values exactly than
        floating point numbers.

        If the number consists of digits only, "JSON" will try to represent
        it as an integer value. If that fails, it will try to represent it
        as a numeric (floating point) value if that is possible without loss
        of precision. Otherwise it will preserve the number as a string
        value (in which case you lose roundtripping ability, as the JSON
        number will be re-encoded to a JSON string).

        Numbers containing a fractional or exponential part will always be
        represented as numeric (floating point) values, possibly at a loss
        of precision (in which case you might lose perfect roundtripping
        ability, but the JSON number will still be re-encoded as a JSON
        number).

        Note that precision is not accuracy - binary floating point values
        cannot represent most decimal fractions exactly, and when converting
        from and to floating point, "JSON" only guarantees precision up to
        but not including the least significant bit.

        If the backend is JSON::PP and "allow_bignum" is enable, the big
        integers and the numeric can be optionally converted into
        Math::BigInt and Math::BigFloat objects.

    true, false
        These JSON atoms become "JSON::true" and "JSON::false",
        respectively. They are overloaded to act almost exactly like the
        numbers 1 and 0. You can check whether a scalar is a JSON boolean by
        using the "JSON::is_bool" function.

        If "JSON::true" and "JSON::false" are used as strings or compared as
        strings, they represent as "true" and "false" respectively.

           print JSON::true . "\n";
            => true
           print JSON::true + 1;
            => 1

           ok(JSON::true eq 'true');
           ok(JSON::true eq  '1');
           ok(JSON::true == 1);

        "JSON" will install these missing overloading features to the
        backend modules.

    null
        A JSON null atom becomes "undef" in Perl.

        "JSON::null" returns "undef".

  PERL -> JSON
    The mapping from Perl to JSON is slightly more difficult, as Perl is a
    truly typeless language, so we can only guess which JSON type is meant
    by a Perl value.

    hash references
        Perl hash references become JSON objects. As there is no inherent
        ordering in hash keys (or JSON objects), they will usually be
        encoded in a pseudo-random order that can change between runs of the
        same program but stays generally the same within a single run of a
        program. "JSON" optionally sort the hash keys (determined by the
        *canonical* flag), so the same data structure will serialise to the
        same JSON text (given same settings and version of JSON::XS), but
        this incurs a runtime overhead and is only rarely useful, e.g. when
        you want to compare some JSON text against another for equality.

        In future, the ordered object feature will be added to JSON::PP
        using "tie" mechanism.

    array references
        Perl array references become JSON arrays.

    other references
        Other unblessed references are generally not allowed and will cause
        an exception to be thrown, except for references to the integers 0
        and 1, which get turned into "false" and "true" atoms in JSON. You
        can also use "JSON::false" and "JSON::true" to improve readability.

           to_json [\0,JSON::true]      # yields [false,true]

    JSON::true, JSON::false, JSON::null
        These special values become JSON true and JSON false values,
        respectively. You can also use "\1" and "\0" directly if you want.

        JSON::null returns "undef".

    blessed objects
        Blessed objects are not directly representable in JSON. See the
        "allow_blessed" and "convert_blessed" methods on various options on
        how to deal with this: basically, you can choose between throwing an
        exception, encoding the reference as if it weren't blessed, or
        provide your own serialiser method.

        With "convert_blessed_universally" mode, "encode" converts blessed
        hash references or blessed array references (contains other blessed
        references) into JSON members and arrays.

           use JSON -convert_blessed_universally;
           JSON->new->allow_blessed->convert_blessed->encode( $blessed_object );

        See to convert_blessed.

    simple scalars
        Simple Perl scalars (any scalar that is not a reference) are the
        most difficult objects to encode: JSON::XS and JSON::PP will encode
        undefined scalars as JSON "null" values, scalars that have last been
        used in a string context before encoding as JSON strings, and
        anything else as number value:

           # dump as number
           encode_json [2]                      # yields [2]
           encode_json [-3.0e17]                # yields [-3e+17]
           my $value = 5; encode_json [$value]  # yields [5]

           # used as string, so dump as string
           print $value;
           encode_json [$value]                 # yields ["5"]

           # undef becomes null
           encode_json [undef]                  # yields [null]

        You can force the type to be a string by stringifying it:

           my $x = 3.1; # some variable containing a number
           "$x";        # stringified
           $x .= "";    # another, more awkward way to stringify
           print $x;    # perl does it for you, too, quite often

        You can force the type to be a number by numifying it:

           my $x = "3"; # some variable containing a string
           $x += 0;     # numify it, ensuring it will be dumped as a number
           $x *= 1;     # same thing, the choice is yours.

        You can not currently force the type in other, less obscure, ways.

        Note that numerical precision has the same meaning as under Perl (so
        binary to decimal conversion follows the same rules as in Perl,
        which can differ to other languages). Also, your perl interpreter
        might expose extensions to the floating point numbers of your
        platform, such as infinities or NaN's - these cannot be represented
        in JSON, and it is an error to pass those in.

    Big Number
        If the backend is JSON::PP and "allow_bignum" is enable, "encode"
        converts "Math::BigInt" objects and "Math::BigFloat" objects into
        JSON numbers.

JSON and ECMAscript
    See to "JSON and ECMAscript" in JSON::XS.

JSON and YAML
    JSON is not a subset of YAML. See to "JSON and YAML" in JSON::XS.

BACKEND MODULE DECISION
    When you use "JSON", "JSON" tries to "use" JSON::XS. If this call
    failed, it will "uses" JSON::PP. The required JSON::XS version is *2.2*
    or later.

    The "JSON" constructor method returns an object inherited from the
    backend module, and JSON::XS object is a blessed scalar reference while
    JSON::PP is a blessed hash reference.

    So, your program should not depend on the backend module, especially
    returned objects should not be modified.

     my $json = JSON->new; # XS or PP?
     $json->{stash} = 'this is xs object'; # this code may raise an error!

    To check the backend module, there are some methods - "backend", "is_pp"
    and "is_xs".

      JSON->backend; # 'JSON::XS' or 'JSON::PP'
  
      JSON->backend->is_pp: # 0 or 1
  
      JSON->backend->is_xs: # 1 or 0
  
      $json->is_xs; # 1 or 0
  
      $json->is_pp; # 0 or 1

    If you set an environment variable "PERL_JSON_BACKEND", the calling
    action will be changed.

    PERL_JSON_BACKEND = 0 or PERL_JSON_BACKEND = 'JSON::PP'
        Always use JSON::PP

    PERL_JSON_BACKEND == 1 or PERL_JSON_BACKEND = 'JSON::XS,JSON::PP'
        (The default) Use compiled JSON::XS if it is properly compiled &
        installed, otherwise use JSON::PP.

    PERL_JSON_BACKEND == 2 or PERL_JSON_BACKEND = 'JSON::XS'
        Always use compiled JSON::XS, die if it isn't properly compiled &
        installed.

    PERL_JSON_BACKEND = 'JSON::backportPP'
        Always use JSON::backportPP. JSON::backportPP is JSON::PP back port
        module. "JSON" includes JSON::backportPP instead of JSON::PP.

    These ideas come from DBI::PurePerl mechanism.

    example:

     BEGIN { $ENV{PERL_JSON_BACKEND} = 'JSON::PP' }
     use JSON; # always uses JSON::PP

    In future, it may be able to specify another module.

USE PP FEATURES EVEN THOUGH XS BACKEND
    Many methods are available with either JSON::XS or JSON::PP and when the
    backend module is JSON::XS, if any JSON::PP specific (i.e. JSON::XS
    unsupported) method is called, it will "warn" and be noop.

    But If you "use" "JSON" passing the optional string "-support_by_pp", it
    makes a part of those unsupported methods available. This feature is
    achieved by using JSON::PP in "de/encode".

       BEGIN { $ENV{PERL_JSON_BACKEND} = 2 } # with JSON::XS
       use JSON -support_by_pp;
       my $json = JSON->new;
       $json->allow_nonref->escape_slash->encode("/");

    At this time, the returned object is a "JSON::Backend::XS::Supportable"
    object (re-blessed XS object), and by checking JSON::XS unsupported
    flags in de/encoding, can support some unsupported methods - "loose",
    "allow_bignum", "allow_barekey", "allow_singlequote", "escape_slash" and
    "indent_length".

    When any unsupported methods are not enable, "XS de/encode" will be used
    as is. The switch is achieved by changing the symbolic tables.

    "-support_by_pp" is effective only when the backend module is JSON::XS
    and it makes the de/encoding speed down a bit.

    See to "JSON::PP SUPPORT METHODS".

INCOMPATIBLE CHANGES TO OLD VERSION
    There are big incompatibility between new version (2.00) and old (1.xx).
    If you use old "JSON" 1.xx in your code, please check it.

    See to "Transition ways from 1.xx to 2.xx."

    jsonToObj and objToJson are obsoleted.
        Non Perl-style name "jsonToObj" and "objToJson" are obsoleted (but
        not yet deleted from the source). If you use these functions in your
        code, please replace them with "from_json" and "to_json".

    Global variables are no longer available.
        "JSON" class variables - $JSON::AUTOCONVERT, $JSON::BareKey, etc...
        - are not available any longer. Instead, various features can be
        used through object methods.

    Package JSON::Converter and JSON::Parser are deleted.
        Now "JSON" bundles with JSON::PP which can handle JSON more properly
        than them.

    Package JSON::NotString is deleted.
        There was "JSON::NotString" class which represents JSON value
        "true", "false", "null" and numbers. It was deleted and replaced by
        "JSON::Boolean".

        "JSON::Boolean" represents "true" and "false".

        "JSON::Boolean" does not represent "null".

        "JSON::null" returns "undef".

        "JSON" makes JSON::XS::Boolean and JSON::PP::Boolean is-a relation
        to JSON::Boolean.

    function JSON::Number is obsoleted.
        "JSON::Number" is now needless because JSON::XS and JSON::PP have
        round-trip integrity.

    JSONRPC modules are deleted.
        Perl implementation of JSON-RPC protocol - "JSONRPC ",
        "JSONRPC::Transport::HTTP" and "Apache::JSONRPC " are deleted in
        this distribution. Instead of them, there is JSON::RPC which
        supports JSON-RPC protocol version 1.1.

  Transition ways from 1.xx to 2.xx.
    You should set "suport_by_pp" mode firstly, because it is always
    successful for the below codes even with JSON::XS.

        use JSON -support_by_pp;

    Exported jsonToObj (simple)
          from_json($json_text);

    Exported objToJson (simple)
          to_json($perl_scalar);

    Exported jsonToObj (advanced)
          $flags = {allow_barekey => 1, allow_singlequote => 1};
          from_json($json_text, $flags);

        equivalent to:

          $JSON::BareKey = 1;
          $JSON::QuotApos = 1;
          jsonToObj($json_text);

    Exported objToJson (advanced)
          $flags = {allow_blessed => 1, allow_barekey => 1};
          to_json($perl_scalar, $flags);

        equivalent to:

          $JSON::BareKey = 1;
          objToJson($perl_scalar);

    jsonToObj as object method
          $json->decode($json_text);

    objToJson as object method
          $json->encode($perl_scalar);

    new method with parameters
        The "new" method in 2.x takes any parameters no longer. You can set
        parameters instead;

           $json = JSON->new->pretty;

    $JSON::Pretty, $JSON::Indent, $JSON::Delimiter
        If "indent" is enable, that means $JSON::Pretty flag set. And
        $JSON::Delimiter was substituted by "space_before" and
        "space_after". In conclusion:

           $json->indent->space_before->space_after;

        Equivalent to:

          $json->pretty;

        To change indent length, use "indent_length".

        (Only with JSON::PP, if "-support_by_pp" is not used.)

          $json->pretty->indent_length(2)->encode($perl_scalar);

    $JSON::BareKey
        (Only with JSON::PP, if "-support_by_pp" is not used.)

          $json->allow_barekey->decode($json_text)

    $JSON::ConvBlessed
        use "-convert_blessed_universally". See to convert_blessed.

    $JSON::QuotApos
        (Only with JSON::PP, if "-support_by_pp" is not used.)

          $json->allow_singlequote->decode($json_text)

    $JSON::SingleQuote
        Disable. "JSON" does not make such a invalid JSON string any longer.

    $JSON::KeySort
          $json->canonical->encode($perl_scalar)

        This is the ascii sort.

        If you want to use with your own sort routine, check the "sort_by"
        method.

        (Only with JSON::PP, even if "-support_by_pp" is used currently.)

          $json->sort_by($sort_routine_ref)->encode($perl_scalar)
 
          $json->sort_by(sub { $JSON::PP::a <=> $JSON::PP::b })->encode($perl_scalar)

        Can't access $a and $b but $JSON::PP::a and $JSON::PP::b.

    $JSON::SkipInvalid
          $json->allow_unknown

    $JSON::AUTOCONVERT
        Needless. "JSON" backend modules have the round-trip integrity.

    $JSON::UTF8
        Needless because "JSON" (JSON::XS/JSON::PP) sets the UTF8 flag on
        properly.

            # With UTF8-flagged strings

            $json->allow_nonref;
            $str = chr(1000); # UTF8-flagged

            $json_text  = $json->utf8(0)->encode($str);
            utf8::is_utf8($json_text);
            # true
            $json_text  = $json->utf8(1)->encode($str);
            utf8::is_utf8($json_text);
            # false

            $str = '"' . chr(1000) . '"'; # UTF8-flagged

            $perl_scalar  = $json->utf8(0)->decode($str);
            utf8::is_utf8($perl_scalar);
            # true
            $perl_scalar  = $json->utf8(1)->decode($str);
            # died because of 'Wide character in subroutine'

        See to "A FEW NOTES ON UNICODE AND PERL" in JSON::XS.

    $JSON::UnMapping
        Disable. See to MAPPING.

    $JSON::SelfConvert
        This option was deleted. Instead of it, if a given blessed object
        has the "TO_JSON" method, "TO_JSON" will be executed with
        "convert_blessed".

          $json->convert_blessed->encode($blessed_hashref_or_arrayref)
          # if need, call allow_blessed

        Note that it was "toJson" in old version, but now not "toJson" but
        "TO_JSON".

TODO
    example programs

THREADS
    No test with JSON::PP. If with JSON::XS, See to "THREADS" in JSON::XS.

BUGS
    Please report bugs relevant to "JSON" to <makamaka[at]cpan.org>.

SEE ALSO
    Most of the document is copied and modified from JSON::XS doc.

    JSON::XS, JSON::PP

    "RFC4627"(<http://www.ietf.org/rfc/rfc4627.txt>)

AUTHOR
    Makamaka Hannyaharamitu, <makamaka[at]cpan.org>

    JSON::XS was written by Marc Lehmann <schmorp[at]schmorp.de>

    The release of this new version owes to the courtesy of Marc Lehmann.

COPYRIGHT AND LICENSE
    Copyright 2005-2013 by Makamaka Hannyaharamitu

    This library is free software; you can redistribute it and/or modify it
    under the same terms as Perl itself.