docs: public static Matcher<AssignmentTree> assignment(
        final Matcher<ExpressionTree> variableMatcher,
        final Matcher<? super ExpressionTree> expressionMatcher) {
      return new Matcher<AssignmentTree>() {
        @Override
        public boolean matches(AssignmentTree t, VisitorState state) {
          return variableMatcher.matches(t.getVariable(), state)
              && expressionMatcher.matches(t.getExpression(), state);
        }
      };
    }