OTS11 — OTS-RTF: Progapation Context and sub-transactions

The OTS specification (ptc/00-10-03) 10.2.2 suggests that
parent transaction ids are not received (or even
propagated):

"When nested transactions are used, the transaction context
remembers the stack of nested transactions started within a
particular execution environment (e.g., process) so that when
a subtransaction ends, the transaction context of the thread
is restored to the context in effect when the subtransaction
was begun. When the context is transferred between execution
environments, the received context refers only to one
particular transaction, not a stack of transactions."

But the description of the PropagationContext in 10.5.2 (on
p10-75) suggests that the parent transaction ids get
propagated as well:

"TransIdentity parents
A sequence of TransIdentity structures representing the
parent(s) of the current transaction. The ordering of the
sequence starts at the parent of the current transaction
and includes all ancestors up to the top-level transaction.
An implementation that does not support nested transactions
would send an empty sequence. This allows a non-nested
transaction implementation to know when a nested transaction
is being imported. It also supports efficient (local)
execution of the Coordinator operations which test parentage
when the importing Transaction Service does interposition."

What is a compliant implementation using PropagationContexts
supposed to do?