> For the complete documentation index, see [llms.txt](https://muradkarakas.gitbook.io/sodium_documentation/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://muradkarakas.gitbook.io/sodium_documentation/language-reference/lexical-elements/identifiers.md).

# Identifiers

Identifiers are sequences of characters used for naming variables, functions, new data types, and preprocessor macros. You can include letters, decimal digits, and the underscore character `_` in identifiers.

The first character of an identifier cannot be a digit.

Lowercase letters and uppercase letters are distinct, such that foo and FOO are two different identifiers.