Presently reads: "If date values are for instance grouped by minutes, all dates or times that are within the same minute are within one group."

Err, but that makes it sound like being within 60 seconds of another value is a default setting.

As far as I can tell, there is no default setting for table:grouped-by.

That is in the absence of a value, there is no basis for grouping. Yes?

Suggest that we drop the note and clarify if there is a default or not.

From ISO 26300:

****
The table:grouped-by attribute specifies the grouping of the date values. Date values can be
grouped by seconds, minutes, hours, days, months, quarters or years. It date values are for
instance grouped by minutes, all dates or times that are within the same minute are within one
group. That, is if the dates 2004-08-27T12:34:46, 2004-08-27T12:34:56 and 2004-08-
27T12:35:46 are given, the first two would be within one group, while the last date would be a
group of its own.
****

That makes it sound like minutes can only be one minute in the minute setting.