Punctuation marks are symbols that organize the structure and meaning of written text. They include periods, commas, exclamation marks, question marks, parentheses, quotation marks, and many others. In typesetting, especially for CJK (Chinese, Japanese, Korean) languages, punctuation handling is particularly complex and directly affects character counting and line wrapping.

Punctuation systems differ significantly between languages. Japanese uses full-width marks such as the period "。" and comma "、," each occupying one full character width. English uses half-width marks like "." and "," followed by a space. This difference directly impacts character counts: the same content expressed in Japanese and English will have different proportions of characters devoted to punctuation.

Japanese typesetting rules (JIS X 4051) specify precise spacing around punctuation. For example, a half-width space follows periods and commas, while no space appears inside brackets. On the web, CSS properties like font-feature-settings and text-spacing-trim are beginning to support these adjustments, though browser support remains incomplete.

Line-break rules (kinsoku processing) are an important aspect of punctuation handling. Periods and commas must not appear at the start of a line (head prohibition), and opening brackets must not appear at the end of a line (tail prohibition). CSS properties word-break and line-break control this behavior, with line-break: strict required for full Japanese line-break compliance.

On social media and messaging platforms, punctuation counting becomes a practical concern. On X (formerly Twitter), every punctuation mark counts as one character toward the 280-character limit, so users must decide how much punctuation to include. Omitting punctuation to save characters has become common in casual social media posts, particularly among younger users. Typography books on Amazon explore these conventions in depth.

In programming, punctuation marks carry syntactic meaning. Semicolons, curly braces, square brackets, dots, and colons are all language syntax elements. Accidentally typing a full-width punctuation mark instead of a half-width one causes compilation errors. This is a common pitfall for developers working with input methods that switch between full-width and half-width modes.