Its type must be a <a href="#Type_definitions">defined</a> type <code>T</code> or a
pointer to a defined type <code>T</code>, possibly followed by a list of type parameter
names <code>[P1, P2, …]</code> enclosed in square brackets.
<code>T</code> is called the receiver <i>base type</i>. A receiver base type cannot be
a pointer or interface type and it must be defined in the same package as the method.