Unclear conformance requirements in section 9.2.3 "Conformance issues" [line 677]
For "Precision" bullet point [line 682]: reads more like a recommendation that probably belongs best in the body of the specification ( also, missing question mark).
For "Time Zones and UTC" [line 684] : it is unclear how these details "restrict the variability inherent in the expressions of Date and Time ": there are several "may" statements normative requirements, and one "cannot". It would be clearer if normative keywords were used (MAY, MAY NOT). Even so, such optional keywords are difficult to interpret in a conformance clause: they sound more like "relaxation" than restrictions - (and a conformance clause is not supposed to relax normative requirements) as stated in the body.