title_body: Can a custom column with "Date" type be added to the tag browser? In Calibre, I created a custom column with the type "Date". While it gets displayed as column in the ebook list, it does not appear in the tag browser.
  
  Is there a way to have a date-based column as category in the tag browser?
  
  It would be great to be able to filter ebooks by years, e.g.:
  
  Year [7]
    1970s [4]
      [1] 1974
      [8] 1975
      [2] 1976
      [1] 1977
    1980s [2]
      [2] 1984
      [2] 1985
    1990s [1]
      [3] 1994
upvoted_answer: Yes, you can accomplish that using SubGroups in Calibre. The way to do a subgroup is described here (for user entered Genres) but I'll do the TL;DR below for how to do it with publication dates: https://manual.calibre-ebook.com/sub_groups.html
  
  
  Create a custom column with desired lookup name (yearpub) and heading and give the column type "Column built from other columns, behaves like tags"
  In the Template box, enter this code: {pubdate:'test($,
  strcat(substr(format_date($,'yyyy'), 0, 3), '0.',format_date($,'yyyy')),
  'Unknown')'}
  Set "Sort/search columb by" to TEXT and mark a check in the "Show in tags browser".
  After restarting Calibre, go to Preferences-->Look and Feel-->Tag Browser and in the entry "Categories with hierarchical items" enter your custom column's lookup name.
  
  
  Now, what that all does is takes the Published Date data of that book/entry and puts it in the format of an hierarchical tag by decade.year which will now show in the Tags Browser under the lookup name you gave, then the decade, then the year. All without having to enter in any extra data! Just make sure the published date is correct. If no published date is given it will mark it as Unknown.
  
  Enjoy!