Legal characters in ISO sortable date format

Question

What are the valid characters for an ISO date? I know of 0 through 9, -, :, T and Z. Are there any more?

I obtain this sortable date format in .NET with .NET's XML serialization and like this:

var stringDate = myDateTime.ToString("s");

Answer 1

It looks like you can also have a W as part of the ISO week date.

You can have a , or . when dealing with decimal fractions that are added to a time element (See the times section here):

To denote "14 hours, 30 and one half minutes", do not include a seconds figure. Represent it as "14:30,5", "1430,5", "14:30.5", or "1430.5".

+ is valid when using them with UTC offsets such as 22:30+04 or 1130-0700.

Durations can use a bunch of letters such as P, Y, M, W, D, T, H, M, and S. They are a component of time intervals and define the amount of intervening time in a time interval.

Time intervals are the last one and can use / to split a start and end time.

It looks like the default format when using the s format string on a datetime is yyyy-MM-ddTHH:mm:ss", so the only valid characters in this case would be 0 to 9, -, : and T. The other characters above are part of the ISO 8601 standard which the sortable date/time pattern follows, but might not be applicable unless you deal with a different format string or culture.