This pattern handles all the target IPv6 addresses by:
1. Using alternation (|) to match different formats
2. First alternative matches the full and compressed zero forms
3. Second alternative matches addresses with double colons
4. Special case for IPv4-mapped address
5. Handles loopback address ::1
6. Anchors (^$) ensure exact matches
The pattern is carefully constructed to match only the valid target addresses and avoid matching invalid ones in the text.