indentation

Indentation is the use of horizontal space at the beginning of a line to indicate structure, hierarchy, or grouping within text or code. In prose and typography, indentation most commonly marks the start of a new paragraph or a quoted block and helps readers parse rhythm and organization.

In traditional text, the first-line indent is a fixed amount of space, often about 0.5 inches (1.27 cm) in printed formats, though exact measurements vary by language, publication, and style guide. Some styles use hanging indents for bibliographies, where the first line is flush and subsequent lines are indented.

In computer programming, indentation serves as a visual cue for code blocks. In many languages (such as Python), indentation is semantically significant, determining block structure; in others (C, Java, JavaScript), braces delimit blocks and indentation is primarily for readability. This has led to debates about spaces versus tabs, with guidelines such as PEP 8 recommending 4 spaces per indentation level and avoiding mixing spaces and tabs.

In data formats and markup, indentation expresses nesting without changing the content. YAML relies on indentation to denote hierarchical structure, while JSON ignores whitespace for data values and HTML uses indentation only for source readability.

Accessibility and readability considerations encourage consistent indentation and alignment. Irregular or excessive indentation can hinder scanning and increase cognitive load, especially for readers with dyslexia or other reading differences.

Historically, indentation has evolved from manuscript practices to modern styles, reflecting the balance between visual clarity and typographic conventions across different languages and domains.