The original instructions weren't terribly clear.

Here's what you do. First type this: [tri.g.ge.r] without the periods.

Then just type your text. At the end type: [/tr.i.gg.er] without the periods. That will cause all your text between those two trigger thingies to be hidden. I had to add the periods to prevent it from creating the hidden message!

Don't forget the brackets.