To declare a method, test, add it to a gmSL block:

<gmSL namespace="gmSL" class="gm"><[CDATA[[
void test(string arg1)
{
        System.LogMessage("Here i am: " + arg1);
}
]]></gmsl>

To run a method, invoke it with a RunCommand statement, using a gm. prefix. For example:

<RunCommand id="gm.test" Prams="Mark" />