javadoc for ISODateTimeFormat.dateTime()

The javadoc for org.joda开发者_JAVA百科.time.format.ISODateTimeFormat.dateTime() is:

Returns a formatter that combines a full date and time, separated by a 'T' (yyyy-MM-dd'T'HH:mm:ss.SSSZZ). The time zone offset is 'Z' for zero, and of the form '±HH:mm' for non-zero.

It is not clear to me where the word 'zero' is pointing at/to. Zero where or what? Is it me or is this sentence unclear?

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the zero is referring to the time zone offset ZZ. ie. for a zero time zone offset (UTC), you would use the Z and write 2009-11-20T11:08:00.000Z; for +8 hours time zone offset, you would write 2009-11-20T11:08:00.000+08:00.