FieldName     = identifier .
Element       = Expression | LiteralValue .
</pre>

<p>
The LiteralType's <a href="#Core_types">core type</a> <code>T</code>
must be a struct, array, slice, or map type
(the syntax enforces this constraint except when the type is given
as a TypeName).
The types of the elements and keys must be <a href="#Assignability">assignable</a>
to the respective field, element, and key types of type <code>T</code>;