Type declarations come in two forms: alias declarations and type definitions.
</p>

<pre class="ebnf">
TypeDecl = "type" ( TypeSpec | "(" { TypeSpec ";" } ")" ) .
TypeSpec = AliasDecl | TypeDef .
</pre>

<h4 id="Alias_declarations">Alias declarations</h4>

<p>
An alias declaration binds an identifier to the given type
[<a href="#Go_1.9">Go 1.9</a>].

        regarding when retracing needs to occur by implementing the Tracing
        Protocol available through
        `tf.types.experimental.SupportsTracingProtocol`.
    *   `TypeSpec` classes (as associated with `ExtensionTypes`) also implement
        the Tracing Protocol which can be overridden if necessary.
    *   The newly introduced `reduce_retracing` option also uses the Tracing