A Trigger Function contains Trigger code that can be called wherever it is needed. It's used to modularize your code and reusing it.
There are 4 function types existing:
There is nothing that is given back by the function and it may use parameters. This function will appear in the trigger action list.
A boolean is given back. This function will appear in the trigger condition list.
This function will appear in the trigger event list. Currently (patch 1.3.3), custom events cannot be used as other events, they will cause script errors.
Some value is given back which is not a boolean and it may use parameters. This function will appear in the trigger function list depending on which data type it returns (e.g. integer, unit, location, point, text).
If something is set to be returned, your code needs to have a return action for every possible case.
This text will be displayed in the editor, if the function is used in the Galaxy Editor. Parameter names are only shown, if they have no default value.
TODO: example picture
The hint text of this function which should contain a description what this function does. It is displayed when the function is selected by user.
Custom Script Code
You can write Galaxy Code here directly. TODO: which code is executed?
How to create a Trigger Function
Right click inside your left lower window (tree) and chose "new" or hit the corresponding button on top of the trigger module's main window.