A mark allows to name a point within a zettel.
This is useful if you want to reference some content in a zettel, either with a [[link|00001007040310]] or with an [[inline-mode transclusion|00001007040324]].

A mark begins with a left square bracket, followed by an exclamation mark character (""''!''"", U+0021).
Now the optional mark name follows.
It is a (possibly empty) sequence of Unicode letters, Unicode digits, the hyphen-minus character (""''-''"", U+002D), or the low-line character (""''_''"", U+005F).
An optional text to be explicitly marked is introduced with a vertical bar character (""''|''"", U+007C), followed by some [[inline-structured elements|00001007040000]].
The mark element ends with a right square bracket.

Examples:
* ``[!]`` is a mark without a name, the empty mark.
* ``[!mark]`` is a mark with the name ""mark"".
* ``[!|some text]``is the empty mark with ""some text"".
* ``[!mark|some text]``is a mark with the name ""mark"" and with ""some text"" that is marked.