Okay, it’s remarkably lame, but here’s my first TiddlyWiki plugin. It defines a new shout macro - you include <<shout some-message>> in a tiddler and it includes A SHOUTING VERSION OF THE MESSAGE.
I adapted it from the sparklines plugin. The important code is at the end - you create a macro by defining a value config.macros.helloWorld, then you simply implement config.macros.helloWorld.handler. This function receives a place variable, defining where the macro will go, and the parameters that were passed into the macro (params).
(removed during jekyll conversion)