DTV12 — what is the year of weekdays?

Specification: Date Time Vocabulary v1.1

Title: what is the year of weekdays?

Summary:

In clause 12.2, the year of weekdays is defined as:

Definition: the finite time scale that has granularity 1 day and that has cardinality 366 and that repeats over the year of days scale

Since the year of days also has 366 time points, it is impossible that the year of weekdays can repeat over it. The intent must be that it repeats over the Gregorian days scale. But that also describes the year of days scale. So it is inadequate.

The Necessity provides the real delimiting characteristic:

Necessity: Each time interval that is an instance of the first time point of the year of weekdays is a Monday and is an instance of a day of year that has an index that is less than 8.

Now, if the intent is that the year of week days goes from the first Monday of one year to the Sunday before the first Monday of the following year (which is not at all clear from the above), then the scale must have 371 (7 x 53) time points, because a year that starts on a Monday ends on a Monday, and the first Monday of the following year is 6 days later.

This structure has no relationship to the year of weeks calendar, because the year of weeks starts with the Monday of the week that contains the first Thursday, and 3 times in 7 years, the year of weekdays will begin in week of year 2.

So, what (and why) is the 'year of weekdays'?

The year of weekdays is intended to provide a subdivision of the “week-based year” that is defined by the year of weeks time scale, in order to support relative time coordinates of the week-day form. For that intent, the existing Definition and Necessity are incorrect.
The ISO week-based year concept is introduced in parallel to the Gregorian year, and the weekday of year concept is then defined as a “day of ISO week-based year”.
The revised text below incorporates terms from the resolution to Issue 19574.