Argument definitions have one canonical name, which is always provided in the underlying code. When argument definitions are used in an expression, they often include aliases that make them easier or faster to type.

For example, the mapColumn function has 2 arguments:

The expression argument includes some aliases, namely exp, fn, and function. That means that you can use any of those four options to provide that argument’s value.

So mapColumn name=newColumn fn={string example} is equal to mapColumn name=newColumn expression={string example}.

There’s also a special type of alias which allows you to leave off the argument’s name entirely. The alias for this is an underscore, which indicates that the argument is an unnamed argument and can be provided without explicitly naming it in the expression. The name argument here uses the unnamed alias, which means that you can further simplify our example to mapColumn newColumn fn={string example}.