A citation key references some external material that is part of a bibliographical collection.

Currently, Zettelstore implements this only partially, it is “work in progress”.

However, the syntax is: beginning with a left square bracket and followed by an at sign character (“`@`”, U+0040), the citation key is given.
The key is typically a sequence of letters and digits.
If a comma character (“`,`”, U+002C) or a vertical bar character is given, the following is interpreted as [inline elements](00001007040000).
A right square bracket ends the text and the citation key element.