Removed restrictons on alignmentUnits

Clarified trailingSkip when dfdl:lengthKind is delimited or endOfParent

Removed timing from dfdl:assert.
Expression for dfdl:assert and dfdl:discriminator may only refer to previous or child elements.
Clarified when expression must be evaluated.

Clarified defaulting arrays and separatorPolicy 'required'

Improved description of xxpadCharacter

Changed choicekind enumerations. Added choiceLengthKind

Corrected syntax of expression predicates

Allow packed or bcd calendars to be delimited

Clarified that outputValueCalc ignores infoset.

Other minor changes.

Property expressions must not contain forward references.

Improved descriptions of property types and corrected some properties.

Significant update to Nils and defaults sections.

Dropped dfdl:nilIndicatorPath and dfdl:nilIndicatorIndex

dfdl:missingValueInitiatorPolicy applies to dfdl:element, dfdl:simpleType, dfdl:sequence, dfdl:choice, dfdl:group