Note: This is subject to future work. Errors, ambiguities, and omissions are to be expected.
Most syntaxes for encoding arbitrary data (DTAS) include in their definition a notion of an unordered collection, e.g. dictionaries. Such collections are very useful to represent certain kinds of data. However they need not be defined at the syntax level.
At syntax level, all structures encoded in a text format are ordered, i.e. their parts appear one after another in the direction of the text. Unorderedness is thus a strictly semantic consideration.
Ambiguity of definition of unorderedness often generates issues of incompatibility between syntaxes and is one of the reasons why TAO does not include any special syntax for unordered collections.
Instead in TAO a notion of unorderedness should be imposed on the data either implicitly or explicitly, via type annotations.