Function

From Fmepedia

A Function is a low-level piece of functionality in FME that performs a specific operation on the objects being passed through it. Functions, together with factories, are the building blocks of FME since Workbench transformers are high-level tools that process features by referencing one or more Factories and/or Functions.

An FME Function can be used directly within a Mapping File, for example...

@Tcl2("SUBSTRINGEXTRACTOR_extract 0 0")

Functions have the syntax @<function_name>.