xargs is not a counter example. It is not a shell builtin, it is a program that takes a bunch of string arguments like every other program a shell would call.

xargs -0 -n1 bash -c 'mv $1 ${1//.js/.ts}' --

Everything to the right of xargs is a string argument passed to xargs.

So an identifier representing a function? Isn’t that the same for most languages?