Every zettelmark content consists of a sequence of Unicode codepoints. Unicode codepoints are called in the following as characters.
Characters are encoded with UTF-8.
A line is a sequence of characters, except newline (U+000A) and carraige return (U+000D), followed by a line ending sequence or the end of content.
A line ending is either a newline not followed by a carriage return, a newline followed by a carriage return, or a carriage return. Different line can be finalized by different line endings.
An empty line is an empty sequence of characters, followed by a line ending or the end of content.
The space character is the Unicode codepoint U+0020.