docs: def get_fwhm_tag(expnum, ccd, prefix=None, version='p'):
      """
      Get the FWHM from the VOSpace annotation.
  
      @param expnum:
      @param ccd:
      @param prefix:
      @param version:
      @return:
      """
      uri = get_uri(expnum, ccd, version, ext='fwhm', prefix=prefix)
      if uri not in fwhm:
          key = "fwhm_{:1s}{:02d}".format(version, int(ccd))
          fwhm[uri] = get_tag(expnum, key)
      return fwhm[uri]