```json example

{"sym":"半径"}

{"sym":"Pi","wikidata":"Q167"}

- an object literal with a`"num"` key

- a JSON number

- a JSON string starting with`+`,`-` or the digits`0`-`9`. Using a string

is useful to represent numbers with a higher precision or greater range than

JSON numbers.

- a JSON string literal. Using a string is useful to represent numbers with a

higher precision or greater range than JSON numbers.

An alternate representation of a**number** with no extra metadata is as a

stringfollowing theformat described above.

stringmatching theRegex pattern`/^[+-]?(0|[1-9][0-9]*)(\.[0-9]+)?(\([0-9]+\))?([eE][+-]?[0-9]+)?$/`.

This allows for a shorthand representation of numbers with a higher precision or

greater range than JSON numbers.

```json example

- an object literal with a`"str"` key

- a[JSON string](https://tools.ietf.org/html/rfc7159#section-7) that starts and

ends with**U+0027`'` APOSTROPHE**.

- a JSON string that is not an identifier shorthand or a number, that is a

- a JSON string that is not a symbol shorthand or a number shorthand.

That is:

-`"Hello World"` is a string (it includes a space character which is not allowed in symbols)

-`"HelloWorld"` is a symbol (it does not include a space character)

-`"3.14"` is a number (it is a valid JSON number)

-`"'3.14'"` is a string (it is wrapped with single quotes)

-`"🍎"` is a string

-``"`🍎`"`` is a symbol shorthand (it is wrapped with backticks)

MathJSON strings must be[well formed JSON strings](https://tc39.es/proposal-well-formed-stringify/), which means they must escape surrogate codepoints`U+D800` to`U+DFFF`, control characters`U+0000` to`U+001F`, and the characters**U+0022`'` QUOTATION MARK** and**U+005C`\` REVERSE SOLIDUS** (backslash).

Symbols are JSON strings that represent the names of symbols, variables,

constants, wildcards and functions.

For a JSON string literal to be interpreted as a symbol, it must either

begin and start with a`` ``` (`U+0060` GRAVE ACCENT) or be a

string matching the Regex pattern`/^[a-zA-Z_][a-zA-Z0-9_]*$/`.

Before they are used, JSON escape sequences (such as`\u` sequences,`\\`, etc.)

are decoded.

The symbols are then normalized to the

[Unicode Normalization Form C (NFC)](https://unicode.org/reports/tr15/). They

are stored internally and compared using the Unicode NFC.

For example, these fourJSON strings represent the same symbol:

For example, these fourobject literals represent the same symbol:

-`"A\u030a"`**U+0041`A‌` LATIN CAPITAL LETTER** +**U+030A` ̊` COMBINING RING

-`{ "sym": "A\u030a" }`**U+0041`A‌` LATIN CAPITAL LETTER** +**U+030A` ̊` COMBINING RING

ABOVE**

-`"\u00c5"`**U+00C5`Å` LATIN CAPITAL LETTER A WITH RING ABOVE**

-`"\u0041\u030a"`**U+0041`A‌` LATIN CAPITAL LETTER A** +**U+030A` ̊` COMBINING RING

-`{ "sym": "\u00c5" }`**U+00C5`Å` LATIN CAPITAL LETTER A WITH RING ABOVE**

-`{ "sym": "\u0041\u030a" }`**U+0041`A‌` LATIN CAPITAL LETTER A** +**U+030A` ̊` COMBINING RING

ABOVE**

Symbols conform to a profile of