docs: def define_from_header(cls, image_header):
          """Define class members directly from FITS header.
  
          Parameters
          ----------
          image_header : instance of hdulist.header
              Header content from a FITS file.
  
          """
  
          self = CsuConfiguration()
  
          # declare lists to store configuration of CSU bars
          self._csu_bar_left = []
          self._csu_bar_right = []
          self._csu_bar_slit_center = []
          self._csu_bar_slit_width = []
  
          for i in range(EMIR_NBARS):
              ibar = i + 1
              keyword = 'CSUP{}'.format(ibar)
              if keyword in image_header:
                  self._csu_bar_left.append(image_header[keyword])
              else:
                  raise ValueError("Expected keyword " + keyword + " not found!")
              keyword = 'CSUP{}'.format(ibar + EMIR_NBARS)
              if keyword in image_header:
                  # set the same origin as the one employed for _csu_bar_left
                  self._csu_bar_right.append(341.5 - image_header[keyword])
              else:
                  raise ValueError("Expected keyword " + keyword + " not found!")
              self._csu_bar_slit_center.append(
                  (self._csu_bar_left[i] + self._csu_bar_right[i]) / 2
              )
              self._csu_bar_slit_width.append(
                  self._csu_bar_right[i] - self._csu_bar_left[i]
              )
  
          return self