I reviewed this document as part of the Security Directorate's ongoing
effort to review all IETF documents being processed by the IESG.  These
comments were written primarily for the benefit of the Security Area
Directors.  Document authors, document editors, and WG chairs should
treat these comments just like any other IETF Last Call comments.

While this document pulls in lots of extensions (and their corresponding
Security Considerations), I think it is well-written and detailed enough
to implement.

It mostly references Security Considerations for other documents it depend
on:

[RFC5440] - Path Computation Element (PCE) Communication Protocol (PCEP)
[RFC8231] - Path Computation Element Communication Protocol (PCEP) Extensions for Stateful PCE 
[RFC8253] - PCEPS: Usage of TLS to Provide a Secure Transport for the Path Computation Element Communication Protocol (PCEP) 
[RFC8281] - Path Computation Element Communication Protocol (PCEP) Extensions for PCE-Initiated LSP Setup in a Stateful PCE Model 
[RFC8664] - Path Computation Element Communication Protocol (PCEP) Extensions for Segment Routing
[RFC9603] - Path Computation Element Communication Protocol (PCEP) Extensions for IPv6 Segment Routing
[RFC9350] - IGP Flexible Algorithm

I think this is appropriate and sufficient.

Nit:
   The security considerations described in [RFC5440], [RFC8231],
   [RFC8253], [RFC8281], [RFC8664], [RFC9603] and [RFC9350] in itself.

This is not a sentence. I think you should change "in itself" to something like
"apply to this document as well" or the like.