title_body: How to show all the books under a tag and its subtags?
upvoted_answer: Solution 1
  
  tags:"=Classics.English" or tags:"=Classics.Russian" or tags:"=Classics"
  
  
  can be reduced to 
  
  tags:"~^Classics"
  
  
  It will show all the files whose tags start with "Classics"
  
  Another variation is
  
  tags:"~Classics"
  
  
  If you omit the ^, then it will show those files too whose tags have "Classics" in them, but not necessarily in the beginning. For example 
  
  - Classics
   |__ Russian
   |__ English
  - Children Classics
  - Foreign Classics for University
  
  
  Solution 2
  
  When you click on tag icon
  
  
  
  two times, it shows double plus sign. This happens only for tags that have subtags.
  
  
  
  When this double sign is on, Calibre shows all the books that are tagged with the tag or its subtags.
  
  Solution 3
  
  Use following search expression
  
  tags:"=.&lt;tag name&gt;"
  
  
  For example,
  
  tags:"=.Fiction"