Other Special Characters

Functional modifiers — variable, schema, optional, nullable, and sign characters.

Special characters work alongside structural characters and literals to add functionality or context to an Internet Object document. Each has a specific semantic meaning and modifies the behavior of schemas, values, or parsing.

Special character set

Symbol	Name	Unicode	Context	Application
@	At sign	U+0040	Variable	Prefixed to a name, declares or references a variable
$	Dollar sign	U+0024	Schema	Prefixed to a name, declares or references a schema
?	Question mark	U+003F	Schema	Suffixed to a bare member name, marks the member optional
*	Asterisk	U+002A	Schema	Suffixed to a bare member name, marks the member nullable; bare on its own, makes a schema accept undeclared members. Quoted ("*") it is an ordinary name, in a schema or in data
-	Hyphen / minus	U+002D	Numeric	Marks a negative value
+	Plus	U+002B	Numeric	Marks a positive value

Usage examples

Variable references and schema definitions

# Variable declarations
~ @r: red
~ @g: green
~ @b: blue
# A schema using variables in an inline constraint
~ $schema: {
    name: string,
    email: email,
    joiningDt: date,
    color: {string, choices: [@r, @g, @b]}
}
---
# Data using variable references
~ John Doe, '[email protected]', d'2020-01-01', @r

Schema modifiers

# Optional and nullable member declarations
~ $user: {
    name: string,          # Required member
    email?: string,        # Optional member (may be omitted)
    avatar*: string,       # Nullable member (may be null)
    metadata*?: object,    # Optional and nullable member

    # The suffixes attach to a bare name. A quoted name says the same with options.
    "code:en": { string, optional: T }
}

# A schema that accepts undeclared members
~ $flexible: {
    id: string,
    name: string,
    *                      # Accept additional, undeclared members
}

Numeric signs

# Positive and negative numbers
temperature: +23.5         # Explicit positive
balance: -150.75           # Negative value
elevation: +8848           # Positive integer
debt: -5000                # Negative integer

Character rules

• Context sensitive — a character's meaning depends on its position and context.

• Variable prefix — @ prefixes variable declarations and references.

• Schema prefix — $ prefixes schema definitions and references.

• Schema suffixes — ? and * are suffixed to bare member names in a schema; a quoted name uses the keyed optional: and "null": options instead.

• Bare versus quoted — a special character is only special when written bare. "*" is a member name, not the wildcard; "a?" is a name ending in ?, not an optional a.

• Numeric prefixes — + and - prefix numeric values to indicate sign.

• Case sensitive — all special characters are case-sensitive.

• Reserved usage — these characters are reserved for their specific functions.

See Also

• Definitions — variables and schema references

• Numeric Values — numeric formatting and signs

• Structural Elements — overview of all structural characters