Semantic Check: Unique field considers field = {value} different to field = "value"

[kiryph]

According to http://www.bibtex.org/Format/ field values (tag content) can be written differently in a bibtex file

Title = {{Bib}\TeX} 
Title = "{Bib}\TeX" 
Title = "{Bib}" # "\TeX" 

Since the unique field check is a semantic check, IMHO it should treat them as the same and should report them as non-unique.

Example file

❯ cat unique_field_test.bib
@Manual{BibTool,
  title = 	 {BibTool},
  author =	 {Gerd Neugebauer},
  year =	 "2019"
}
@Manual{BibTool,
  title = 	 "BibTool",
  author =	 {Gerd Neugebauer},
  year =	 "2019"
}
@ARTICLE{article-minimal,
   author = {L[eslie] A. Aamport},
   title = {The Gnats and Gnus Document Preparation System},
   journal = {\mbox{G-Animal\'s} Journal},
   year = 1986
}

❯ bibtool -- 'unique.field{title}' -o '' unique_field_test.bib

~/bibtool-as-linter
❯

I have read the comment https://github.com/ge-ne/bibtool/issues/61#issuecomment-535402283. So I expect that bibtool does not want to treat them this way. Then I would argue bibtool should complain about bibtex files with curly braces that they are not fully supported. Interestingly, the upstream test directory contains bibtex data with curly braces.