code: def gatk_major_version(self):
          
          full_version = self.get_gatk_version()
          # Working with a recent version if using nightlies
          if full_version.startswith("nightly-"):
              return "3.6"
          parts = full_version.split("-")
          if len(parts) == 4:
              appistry_release, version, subversion, githash = parts
          elif len(parts) == 3:
              version, subversion, githash = parts
          elif len(parts) == 2:
              version, subversion = parts
          elif len(parts) == 1:
              version = parts[0]
          # version was not properly implemented in earlier GATKs
          else:
              version = "2.3"
          if version.startswith("v"):
              version = version[1:]
          return version
docs: Retrieve the GATK major version, handling multiple GATK distributions.
  
          Has special cases for GATK nightly builds, Appistry releases and
          GATK prior to 2.3.