Section 6.4.8 of the current ED describes CSSPageRule with only "selectorText" and "style" attributes. (The latter is a list of declarations.) This interface does not expose the margin at-rules:
A "cssRules" attribute of type CSSRuleList should be added, as in CSSMediaRule.
Issue originally filed on Paged Media:
Moved back to https://www.w3.org/Style/CSS/Tracker/issues/260
Per WG resolution, the CSSPageRule will be defined in css3-page: