TIMESTAMPS:

00:00 Introduction
01:43 Aspect ratio demos
03:29 Theory (signal contents)
06:27 Helper signal
07:22 Camera mode
07:54 Film mode
10:28 ColourPlus
12:49 Extra signals (Wide screen signalling / ghost cancellation reference)
14:14 The decline of PALplus
16:06 Inside the PALplus decoder
21:04 Conclusion

Referenced videos:
16mm telecine process:    • 16mm telecine process  
Demonstration: Lining Up Outside Broadcast Cameras:    • Demonstration: Lining Up Outside Broa...  

Other links: https://en.wikipedia.org/wiki/PALplus
PALplus spec: https://www.itu.int/dms_pubrec/itu-r/...