"Force" button on "Research Technology" trigger -- what does it do?

I'm building a scenario on "ludicrous" map size, and decided I'd give everyone the ability to make harbors. That just means making a trigger with an effect "Research Technology" and choosing "Thallassocracy" -- so far so good. But there's a button labeled "Force" for the technology choice, and I have no clue what it does! Once again I'm baffled that they game designers have never published an intensive, thorough guide to triggers and how to use them, so here I am asking you all: what does the "Force" button do?