Issue meta: Cover dates

Capture a cover date in a pub-date element with the attribute pub-type="cover".

issue-meta/pub-date[@pub-type="cover"]

The date captured here must match exactly the cover date found in the article meta for every article in the issue.

In addition, capture a iso-8601-date attribute on the pub-date element. The value of this attribute must have the format YYYY-MM-DD

Determine the value of this attribute as follows:

Content of pub-date	ISO 8601 date
Day, month, year	Use the year, month, and day values for ISO 8601 date.
Month, year	Use the year and month values, and add 01 for the day value. If there is more than one issue in a month, increment the day value by 1 for each following issue in the same month.
Year only	Use the year value, and add 01 for the month value and 01 for the day value.
Double month (e.g. Mar.-Apr.)	Use the month value corresponding to the first named month, e.g. 03 for Mar.-Apr..
Season	Follow the scheduled online publication date for each journal for the day, month and year value.

See Cover dates for further information and examples of cover dates.

<pub-date pub-type="cover" iso-8601-date="2019-12-01" >
  <season>Winter</season>
  <year>2019</year>
</pub-date>