title_body: How to show all the books under a tag and its subtags? Calibre has a feature that lets you create subtags. See "Making subgroups of tags" in the official blog post.
  
  
    Now to actually get hierarchical tags, in the tags section of the metadata entry enter a tag of the form MainTag.SubTag. Like in the top figure on the right and example would be Classics.Russian or Classics.English.
  
  
  Say, I have tags
  
  Classics
  |__ Russian
  |__ English
  
  
  What search expression should I use to display all the books that are tagged with "Classics" or with its subtags i.e "Classics.English" and "Classics.Russian"?
  
  I can get the result with
  
  tags:"=Classics.English" or tags:"=Classics.Russian" or tags:"=Classics"
  
  
  But its becomes ungainly if there are more than few subtags.
  
  What search expression I should use here?
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"