Links

Just as on POSIX, links come in two flavours: hard links and soft links. Neither is superior; they are suited to different use cases. Each may contain the other; the major difference is if the reference is mutable or immutable.
Hard links are "merely" CIDs. They point directly to the exact bits that the CID represents. If these bits originate on a different account, they are copied into the linking file system.
Soft links are URLs. They are relative to a mutable pointer, such as a DNSlink. They have the advantage of updating along with versions, but are more liable to break.

Comparison

Hard Links
Soft Links
Type
CID
URL
Mechanism
Copy
Reference
Mutability
Immutable
Mutable
Availability Guarantee
Self-validating
Subpaths
Cycles
Auto-update
Web 2 Compatible