# Choosing names and recognizing keywords

[Syntax and values](README.md)

An **identifier** is a name you choose for a variable or function. A **keyword**, such as `if`, already has a special job in the language and is reserved for that job. **Case-sensitive** means capital letters matter: `score` and `Score` are different names.

The technical character rules below let you use names from many languages and some emoji. **ASCII** is an older, small character set containing basic Latin letters, digits `0` through `9`, and common punctuation. **Unicode** covers many more writing systems. Its category `Other_Symbol` includes pictorial symbols such as many emoji.

A **combining mark** adds something to a character, such as an accent. Emoji can also contain extra parts: a **presentation selector** asks for a text or colorful emoji appearance, a **skin-tone modifier** changes a person's tone, and **tag characters** help specify certain flags. A **zero-width joiner** is an invisible link joining supported emoji parts into one displayed symbol. These are rules for recognizing the whole name; you do not need to type invisible characters yourself. Short, clear names such as `score` are a good starting point.

Identifiers are case-sensitive. They may start with `_`, a [Unicode](../concepts/unicode.md) letter, or
a Unicode `Other_Symbol` character such as an ordinary emoji. Later characters
may also include Unicode decimal digits and combining marks.

Emoji presentation selectors, skin-tone modifiers, tag characters, and valid
zero-width-joiner emoji sequences remain part of the same identifier. A
zero-width joiner is accepted only between emoji symbol components; it cannot
act as an invisible separator in an ordinary identifier. An emoji sequence
whose first source character is an ASCII digit or `#` cannot start an
identifier because those characters retain their number and comment meanings.

Valid examples include:

```text
score
player2
_temporary
café
🚀
score🚀
👩‍💻
```

An ASCII digit cannot start an identifier. Hyphens are subtraction operators,
not identifier characters, so use `highScore` or `high_score`, not
`high-score`.

English keywords are reserved and cannot be used as identifiers in English
source:

| Keywords | | | |
|---|---|---|---|
| `use` | `let` | `set` | `if` |
| `else` | `while` | `for` | `in` |
| `function` | `return` | `when` | `true` |
| `false` | `none` | `and` | `or` |
| `not` | | | |

Standard-library names such as `say` and `forward` are not keywords. They are
ordinary, shadowable names supplied by the selected locale.

## Related entries

[Syntax and values](README.md) · [Built-ins](../builtins/README.md) · [Programming guides](../guides/README.md)