keywords-function

A function is a basically a command that returns a value. It may or may not change something in some manner. Each function must have a returns clause. Use the return keyword to return the value. See the section on [Functions] for more information.

\function\ identifier [OptionalDeclarationSequence]
    \returns\ TypeName
  ' Whatever the function does should be here
  \return\ SomeValue

For more on declaration sequences, see Declaration sequence.