depth header

In WebDAV methods where there can be a Depth header, the rule is :
"0" : the method applies only to the resource
"1" : to the resource and its immediate children
"infinity" : to the resource and all its progeny

Ok, but what does it mean for a collection, that contains usually many resources : does the  1 or infinity give informations about the resources/files in the collection/directory ?
It's not clear for me...