2Preliminaries

2.1Characters and lines

Any sequence of characters is a valid CommonMark document.

A character is a Unicode code point. Although some code points (for example, combining accents) do not correspond to characters in an intuitive sense, all code points count as characters for purposes of this spec.

This spec does not specify an encoding; it thinks of lines as composed of characters rather than bytes. A conforming parser may be limited to a certain encoding.

A line is a sequence of zero or more characters other than line feed (U+000A) or carriage return (U+000D), followed by a line ending or by the end of file.

A line ending is a line feed (U+000A), a carriage return (U+000D) not followed by a line feed, or a carriage return and a following line feed.

A line containing no characters, or a line containing only spaces (U+0020) or tabs (U+0009), is called a blank line.

The following definitions of character classes will be used in this spec:

A Unicode whitespace character is a character in the Unicode Zs general category, or a tab (U+0009), line feed (U+000A), form feed (U+000C), or carriage return (U+000D).

Unicode whitespace is a sequence of one or more Unicode whitespace characters.

A tab is U+0009.

A space is U+0020.

An ASCII control character is a character between U+0000–1F (both including) or U+007F.

An ASCII punctuation character is !, ", #, $, %, &, ', (, ), *, +, ,, -, ., / (U+0021–2F), :, ;, <, =, >, ?, @ (U+003A–0040), [, \, ], ^, _, ` (U+005B–0060), {, |, }, or ~ (U+007B–007E).

A Unicode punctuation character is a character in the Unicode P (puncuation) or S (symbol) general categories.