Each Ractive instance has a
transitions property, which contains transition functions specific to that instance.
When an element with a specified
outro transition is added or removed, Ractive first looks at
ractive.transitions to see if it can find the right transition function. If it fails, it then looks in
Ractive.transitions (the global transitions registry).
Ordinarily, transitions are added to a Ractive instance as an initialisation option, but it is possible to swap them out after initialisation (for example, if your app determines that the user's browser can't handle a particular transition, or due to a configuration change).