[Tagging] type=multipolygon or boundary?

[Warin]

Hi,
I have examples of National Parks and State Forests etc that were tagged 
with type=multipolygon changed to type=boundary ...

Which is 'correct' ... or are both useable? The wiki is not clear.

The one I am particularly concerned with is relation 5901253 that is not 
correctly rendered. However there are a number of others that have been 
changed ... no changeset notification either.