alias name to the id it stands for, file-local; no record refers to an alias by name
Optionalextensionsthe <Extension> elements of the document's own <Extensions>, each as the XML it is.
Their content is foreign to this schema by design -- a tool stamps whatever it likes there,
such as UaModeler's ModelInfo -- so there is nothing to model and only the bytes to keep.
the first record of a document: what the loader needs before any node