et the rule weight to 1 point

  .BIBLIOGRAPHY_STRING_UNDERLINE 1 3p
      - turn underlining on; set the rule weight to 1 point; set
        the gap between the string and the underline to 3 points
  
  .BIBLIOGRAPHY_STRING_UNDERLINE DOUBLE .75 3p
      - turn double-underlining on; set the rule weight to 3/4 of
        a point; set the gap between the string and the upper
        underline to 3 points; leave the gap between the upper
        and the lower underline at the default
  
  .BIBLIOGRAPHY_STRING