code: def validate_tag(self, tag_name, prefix=None):
          
          new_version = semantic_version(tag_name)
          current = self.latest()
          if current:
              tag_name = current['tag_name']
              if prefix:
                  tag_name = tag_name[len(prefix):]
              tag_name = semantic_version(tag_name)
              if tag_name >= new_version:
                  what = 'equal to' if tag_name == new_version else 'older than'
                  raise GithubException(
                      'Your local version "%s" is %s '
                      'the current github version "%s".\n'
                      'Bump the local version to '
                      'continue.' %
                      (
                          str(new_version),
                          what,
                          str(tag_name)
                      )
                  )
          return current
docs: Validate ``tag_name`` with the latest tag from github
  
          If ``tag_name`` is a valid candidate, return the latest tag from github