The "collection" object is undocumented in the Help.
Optional source for contents from JF Nifenecker:
by JP Ledure (telegram)
The Collection object is indeed useful to know.
The LO implementation looks like the Microsoft/VBA one: https://docs.microsoft.com/en-us/office/vba/language/reference/user-interface-help/collection-object.
The SF Dictionary object is a superset of the Collection object. The implementation in SF is inspired by https://docs.microsoft.com/en-us/office/vba/language/reference/user-interface-help/dictionary-object
Although similar, VBA proposes both mapping classes.
BTW the SF Dictionary uses a Collection internally ...
The implementation of Collections in Basic is defined here as the BasicCollection class:
Rafael Lima committed a patch related to this issue.
It has been pushed to "master":
tdf#145067 Document the Basic Collection object