A substitutable element is one that can replace another element in an instance.
A key point about substitutions is that they are defined by the replacement element, and not by the element that is being replaced. This means, for example, that domains and exchanges may create substitutions for elements in Core…without any modification to the Core schema itself.
The Justice domain defines element
j:PersonHairColorCodewith a code set from the NCIC standard as a substitution for abstract element
PersonHairColorAbstractin Core. The Core namespace is not affected by this substitution.