Add a filter to index by year-month

[yolih]

The default format for output is
/sitemap.xml?yyyy=2019&mm=08&dd=03

and there is an existing filter to move the year to the URL
/sitemap-2019.xml?mm=08&dd=03

But an additional filter that provided the ability to index the document tree by year&month
/sitemap.xml?yyyy=2019&mm=08
or by year would be very useful
/sitemap.xml?yyyy=2019

98212-zen
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[GaryJones]

What's the use case for adding this? What's the intended goal?

[yolih]

The intended goal of indexing by year-month is to consolidate indexed sitemaps into files by month instead of files by day and thereby reducing the total number of indexed sitemaps.

The request for this came from a client with a large number of posts that go back years. The MSM plugin generates a sitemap for each day with published content, and in this case that translates to 4,304 sitemaps. The client is using Google Search Console which only allows visibility of 1000 sitemaps, so they are trying to find a way to have no more than 1000 indexed sitemaps for their site in total.