Primitive type 'st'
The character string data type stands for text data, primarily intended for machine processing (e.g. sorting, querying, indexing, etc.) Used for names, symbols, and formal expressions.
Note that FHIR strings SHALL NOT exceed 1,048,576 (1024*1024) characters in size
All FHIR elements must have a @value or children
hasValue() or (children().count() > id.count())
unique id for the element within a resource (for internal references)
Must have either extensions or value[x], not both