document(..., Key => ...) -- key of a documentation node

The document key is the the name of the node, specifically the one that allows users to find the documentation for the desired command. Some node names, rather than being strings, are sequences of Macaulay 2 objects that refer to specific method functions. If one is documenting a function of Macaulay 2, the key will just be the function's name, as in the documentation for resolution.

Key => resolution,

However, if one is documenting a method for a function, then the key will have a different form, as in the documentation for resolution(Module).

Key => (resolution,Module),

If one is documenting an optional argument to a function, then the key has a different form still, as in resolution(..., SyzygyLimit => ...).

Key => [resolution,SyzygyLimit],

Finally, if one is documenting an overview of a group of functions or a package, as in chain complexes then one would set up a document key of the form:

Key => "chain complexes",

No two documentation nodes may have the same key or even a key which is a synonym for a key which is already used. However, sometimes there is a need for several documentation nodes to have the same key. This happens when a command that needs to be documented is a synonym for another already documented command. In this case the synonym's key should be stated in quotation marks. As an example, look at the documentation for SUBSECTION and HEADER2.