1) Condition.abatement should be an is-modifier = true element (especially since Condition.clinicalStatus is considered an is-modifier element – and it is only optional – so it is possible to have abatement without a clinicalStaus)

Per QA 5c: Ensure all elements (and only those elements) that could change the interpretation of other data are marked as "isModifier"

http://wiki.hl7.org/index.php?title=DSTU_QA_Guidelines

2) Since Condition.clinicalStatus and Condition.abatement are both optional (minOccurs = 0), we should define a default interpretation if one or both are not populated.

Per is-modifier guidance, "Wherever possible, elements labeled "Is-Modifier = true" also have a minimum cardinality of 1, or a default value, in order to introduce certainty in their handling"

http://hl7.org/fhir/2016Sep/conformance-rules.html#isModifier