patterns are registered does not matter.
</p>

<p>
  This change breaks backwards compatibility in small ways, some obvious&mdash;patterns with "{" and "}" behave differently&mdash;
  and some less so&mdash;treatment of escaped paths has been improved.
  The change is controlled by a <a href="/doc/godebug"><code>GODEBUG</code></a> field named <code>httpmuxgo121</code>.

<p>
The language <a href="#Predeclared_identifiers">predeclares</a> certain type names.
Others are introduced with <a href="#Type_declarations">type declarations</a>.
<i>Composite types</i>&mdash;array, struct, pointer, function,
interface, slice, map, and channel types&mdash;may be constructed using
type literals.
</p>

<p>
Each type <code>T</code> has an <i>underlying type</i>: If <code>T</code>

Others are introduced with <a href="#Type_declarations">type declarations</a>
or <a href="#Type_parameter_declarations">type parameter lists</a>.
<i>Composite types</i>&mdash;array, struct, pointer, function,
interface, slice, map, and channel types&mdash;may be constructed using
type literals.
</p>

<p>
Predeclared types, defined types, and type parameters are called <i>named types</i>.