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Various JSON Specifications

Key Changes from RFC 4627 to RFC 7159

JSON Text Flexibility

  • RFC 4627: A JSON text must be either an object or an array.

  • RFC 7159: A JSON text can be any JSON value, including objects, arrays, strings, numbers, booleans, or null.

Unicode Handling

  • RFC 4627: Was less explicit about Unicode handling, particularly for surrogate pairs.

  • RFC 7159: Clarified the handling of Unicode, especially with regards to surrogate pairs, ensuring proper representation and validation.

Number Precision

  • RFC 4627: Did not explicitly state limitations on number precision.

  • RFC 7159: Emphasized that implementations should not expect to process numbers exactly as received if they fall outside of what can be represented by a double-precision floating-point format (IEEE 754).

White Space Handling

  • RFC 4627: Allowed a limited set of whitespace characters (space, tab, newline, carriage return).

  • RFC 7159: Allowed these same characters but provided more clarity on their usage.

Key Changes from RFC 7159 to RFC 8259

Clarifications and Editorial Improvements

  • RFC 8259: Incorporated various editorial improvements and clarifications to enhance readability and precision without altering the technical content.

Consistent Terminology

  • RFC 8259: Ensured consistent terminology and definitions throughout the document.

No Major Technical Changes

  • RFC 8259: Did not introduce major technical changes but focused on consolidating and clarifying the changes introduced in RFC 7159.

Summary of Key Differences

RFC 4627 (2006)

  • JSON text must be an object or array.
  • Less explicit about Unicode handling.
  • No explicit precision constraints on numbers.

RFC 7159 (2014)

  • JSON text can be any JSON value.
  • Clarified Unicode handling, especially surrogate pairs.
  • Advised on number precision and representation.
  • Provided clearer guidance on allowed whitespace.

RFC 8259 (2017)

  • Incorporated editorial improvements from RFC 7159.
  • Ensured consistent terminology and definitions.
  • No major technical changes from RFC 7159.

JSON5 (v1.0.0)

JSON5 is a superset of JSON that aims to alleviate some of the limitations of the original JSON specification by expanding its syntax to include some features from ECMAScript 5.1.

Objects

  • Object keys can be ECMAScript 5.1 IdentifierNames.
  • Objects can have a single trailing comma.

Arrays

  • Arrays can have a single trailing comma.

Strings

  • Strings can be single-quoted.
  • Strings can span multiple lines by escaping new line characters.
  • Strings can include character escapes.

Numbers

  • Numbers can be hexadecimal.
  • Numbers can have a leading or trailing decimal point.
  • Numbers can be IEEE 754 positive infinity, negative infinity, and NaN.
  • Numbers can begin with an explicit plus sign.

Comments

  • Single and multi-line comments are allowed.

White Space

  • Additional white space characters are allowed.

Writing JSON5 Behavior

While TinyJSON is a fully compliant JSON5 parser, its write operations (dump(), write_file()) output standard RFC 8259 JSON by default (with the exception of preserving loaded comments). This makes it highly suitable for converting JSON5 documents into standard JSON.