ok let's make sure we are on same page because there are different things that go on:
FARR plugins usually search with every keypress, and the plugin is called after every keypress.
The search function sent to your plugin actually also tells you whether user hit enter at the end of their search, in case you want to handle that event as the "trigger" specially. This is most useful when you have a plugin that is not showing a list of results but is showing some output in richtext or browser mode.
Now if your plugin is returning standard results as the user types, like internet links, program or data file paths, clipboard text snippets, or internal search strings or aliases, etc., then your plugin never has to worry about triggering anything, since farr will do this automatically.
FARR does call a special trigger function that lets you intercept it's normal "trigger" functionality, both for your own results and results generated by normal search and plugin.
The bottom line is, if the result is returned as a normal FARR result, then you can either let FARR handle the launching of it, or you can catch it with the special trigger function.
If the results are being displayed in richtext or browser mode, then there is no official "TRIGGERING" that gets called -- instead you can either respond to the press of enter by checking the flag in the search function that is called, OR there is a new keypress function that gets called when various keys are pressed that you could use instead (cant remember the names of these functions maybe fscript gurus can help here?)