old_contents: from django.core.validators import RegexValidator
  
  sha1_validator = RegexValidator(regex="^[a-f0-9]{40}$",
                                  message="Must be valid sha1 sum")
  tag_validator = RegexValidator(regex="^[\w\-\.]+$",
                                 message="Must be letters and numbers" +
                                 " separated by dashes, dots, or underscores")
  
new_contents: from django.core.validators import RegexValidator
  
  sha1_validator = RegexValidator(regex="^[a-f0-9]{40}$",
                                  message="Must be valid sha1 sum")
  tag_validator = RegexValidator(regex="^[A-Za-z][\w\-\.]+[A-Za-z]$",
                                 message="Must be letters and numbers" +
                                 " separated by dashes, dots, or underscores")
  
subject: Update tag regex