// Second as decimal number (00-61), allowing for up to two
// leap-seconds (but POSIX-complaint implementations will ignore
// leap seconds).
// TODO: I have no idea what the docs are talking about in relation
// to leap seconds
builder.appendSecondOfDay(2);
break;
// case 'U':
// Week of the year as decimal number (00-53) using Sunday as
// the first day 1 of the week (and typically with the first
// Sunday of the year as day 1 of week 1). The US convention.