The reference says that $x:tt matches "either side of the `=>` in macro_rules` which is technically true but completely uninformative. This changes that bullet point to what the book says (a single token or sequence of token trees inside brackets).
* `ty`: a [type](#types)
* `ident`: an [identifier](#identifiers)
* `path`: a [path](#paths)
-* `tt`: either side of the `=>` in macro rules
+* `tt`: a token tree (a single [token](#tokens) or a sequence of token trees surrounded
+ by matching `()`, `[]`, or `{}`)
* `meta`: the contents of an [attribute](#attributes)
In the transcriber, the