The following data-types are defined for Property values (see PROPERTY_VALUE) and Parameter values (see PARAM_VALUE). Although quite similar, the table indicates where there are necessary differences.
Properties embrace ‘orig-text’ and annotate it with a combination of ‘Key’ and/or ‘Value’ attributes. The ‘Value’ is considered optional if the orig-text contains the same textual representation, and a ‘Key’ is optional in those circumstances where an entity association is not available.
Parameters embrace an explicit ‘value’ and can annotate some cases with a ‘Key’ attribute. The ‘Key’ references are mandatory when interfacing to citation-templates if an object is to be passed. Parameters can also override the ‘value’ formatting using their ‘Subst’ attribute. During local Parameter substitution, the precedence is: ‘Subst’ attribute, any explicit ‘value’ (formatted according to data-type), any entity key name.
Prior to V4.1, a Date Parameter was restricted to ISO Gregorian dates; however, the full range of calendars is required for older sources, and a common example is citing newspapers that predate the Julian-to-Gregorian changeover.