presto-parser/src/main/java/io/prestosql/sql/parser/AstBuilder.java/AstBuilder/visitAtTimeZone
class AstBuilder:    @Override
    public Node visitAtTimeZone(SqlBaseParser.AtTimeZoneContext context)
    {
        return new AtTimeZone(
                getLocation(context.AT()),
                (Expression) visit(context.valueExpression()),
                (Expression) visit(context.timeZoneSpecifier()));
    }