* Section 3.2.3 - I *think* this should read "An intermediary MAY
keep a local copy..." -> "An intermediary MAY be required to keep
a local copy..."
Hm, we thought that the callout should always work, even if the OPES
intermediary does not have enough buffer available to keep a local
copy - simple seems to be more stable and robust. The callout server
can still ask the OPES intermediary to keep a local copy if possible,
but it should not assume the such local copy will always be made. Does
that make sense?