Zettelmarkup: Citation Key
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), a 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. A right square bracket ends the text and the citation key element.