> For the complete documentation index, see [llms.txt](https://docs.internetobject.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.internetobject.org/structure-and-syntax/structural-elements/other-special-characters.md).

# Other Special 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 member name, marks the member optional                                                |
| `*`    | Asterisk       | `U+002A` | Schema   | Suffixed to a member name, marks the member nullable; also makes a schema accept undeclared members |
| `-`    | Hyphen / minus | `U+002D` | Numeric  | Marks a negative value                                                                              |
| `+`    | Plus           | `U+002B` | Numeric  | Marks a positive value                                                                              |

## Usage examples

### Variable references and schema definitions

```ruby
# 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, 'john.doe@example.com', d'2020-01-01', @r
```

### Schema modifiers

```ruby
# 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
}

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

### Numeric signs

```ruby
# 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 member names in a schema.
* **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](/definitions/definitions.md) — variables and schema references
* [Numeric Values](/structure-and-syntax/values/number.md) — numeric formatting and signs
* [Structural Elements](/structure-and-syntax/structural-elements.md) — overview of all structural characters


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter:

```
GET https://docs.internetobject.org/structure-and-syntax/structural-elements/other-special-characters.md?ask=<question>&goal=<endgoal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal.

The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.