The Type of elements within the Array.
This indicates the types of Atom that are acceptable in this
For example an AtomicArray of strings may accept NameAtoms, or
StringAtoms or indeed both.
This is a flags based enum so more than one type may be
indicated by combining values.
The possible values are:.
The AtomicTypes type is a flags type enumeration so different
values can be combined together using bitwise operations. It may
take the following values: