docs: def accession(self):
          """
          Parse accession number from commonly supported formats.
  
          If the defline does not match one of the following formats, the entire
          description (sans leading caret) will be returned.
  
          * >gi|572257426|ref|XP_006607122.1|
          * >gnl|Tcas|XP_008191512.1
          * >lcl|PdomMRNAr1.2-10981.1
          """
          accession = None
          if self.defline.startswith('>gi|'):
              match = re.match('>gi\|\d+\|[^\|]+\|([^\|\n ]+)', self.defline)
              if match:
                  accession = match.group(1)
          elif self.defline.startswith('>gnl|'):
              match = re.match('>gnl\|[^\|]+\|([^\|\n ]+)', self.defline)
              if match:
                  accession = match.group(1)
          elif self.defline.startswith('>lcl|'):
              match = re.match('>lcl\|([^\|\n ]+)', self.defline)
              if match:
                  accession = match.group(1)
          return accession