In the manual, in section 18.19-20, in the rules for printing the announcement of light/darkness, the examples show an ‘instead’—
say "You are almost blinded by the suffusion of white light, and have spots before your eyes." instead.
However, I accidentally typed my rule in my review game without an ‘instead’ and it worked. I tried it with the ‘instead’, and it did the same thing. I did both dark and light, with and without ‘instead’ and didn’t notice a difference…?! Should there have been a difference??
Writing “instead” means that the rule outcome is failure. Without it, the outcome is the default for the rulebook, which in this case happens to be success. But the difference between failure and success is irrelevant here since nothing depends on it. Either outcome has the effect of stopping the rulebook.
Most rulebooks have a default of no outcome. When a rule finishes with no outcome, the rulebook proceeds to its next rule (if any).
I expect that the author of the example forgot that the “for printing the announcement of darkness” rulebook defaults to success. But in any case, it’s easier to write a few unnecessary "instead"s than to remember all the default outcomes for obscure rulebooks.