For an event to occur, it typically needs to complete certain conditions, known as the event trigger
The trigger is a list of one or additional circumstances that has to be true for the event to fire. You can e.g. say that a country occasion should only happen to US, by using a tag trigger:
Scope
There are two types of events, region events and country events. The triggers for a province event will check property of the province in question only, while the triggers of a country event will check country properties. It is therefore probable to have the same trigger code denote two dissimilar things due to the scope. As an example, the trigger can be used in both cases.
There are also ways to alter scope; either from region to country or vice versa, or from one country to one more or from one province to another. What a scope modify does is to perform checks on this other body, and return if they are factual or not.
Numerical Triggers
A incomplete list of the triggers in Discovery_of_the_East_Indian_trade_route reads:
num_of_ports = 4NOT = { mercantilism_freetrade = -2 }
In EU, the equals sign in fact means "equal to or greater than". Use the NOT to mean "less than".
In the example above, the player must have 4 or more port provinces, and their Mercantilism/Freetrade Domestic policies slider must be set to -3 to -5, i.e., less than -2.
Combining Triggers
You can unite more than a few trigger conditions into one activate. This is done on the example above, where we check for country faith and capital location. The universal rule is that if you have several conditions listed, all of them must be satisfied for the trigger to be true.
If we want to have circumstances based on one true out of a set, we use OR = {}.