docs: def crossborder_capacity(network, method, capacity_factor):
      """
      Adjust interconnector capacties.
  
      Parameters
      ----------
      network : :class:`pypsa.Network
          Overall container of PyPSA
      method : string
          Method of correction. Options are 'ntc_acer' and 'thermal_acer'.
          'ntc_acer' corrects all capacities according to values published by 
          the ACER in 2016.
          'thermal_acer' corrects certain capacities where our dataset most 
          likely overestimates the thermal capacity.
      capacity_factor : float
          branch capacity factor. Reduction by branch-capacity 
          factor is applied afterwards and shouln't effect ntc-values, which 
          already include (n-1)-security. To exclude the ntc-capacities from the 
          capacity factor, the crossborder-capacities are diveded by the factor 
          in this function. For thermal-acer this is excluded by setting branch
          capacity factors to one.
          
  
      """         
      if method == 'ntc_acer':
          cap_per_country = {'AT': 4900,
                             'CH': 2695,
                             'CZ': 1301,
                             'DK': 913,
                             'FR': 3593,
                             'LU': 2912,
                             'NL': 2811,
                             'PL': 280,
                             'SE': 217,
                             'CZAT': 574,
                             'ATCZ': 574,
                             'CZPL': 312,
                             'PLCZ': 312,
                             'ATCH': 979,
                             'CHAT': 979,
                             'CHFR': 2087,
                             'FRCH': 2087,
                             'FRLU': 364,
                             'LUFR': 364,
                             'SEDK': 1928,
                             'DKSE': 1928}
  
      elif method == 'thermal_acer':
          cap_per_country = {'CH': 12000,
                              'DK': 4000,
                              'SEDK': 3500,
                              'DKSE': 3500}
          capacity_factor = {'HV': 1, 'eHV':1}
      if not network.lines[network.lines.country != 'DE'].empty:
          weighting = network.lines.loc[network.lines.country!='DE', 's_nom'].\
                  groupby(network.lines.country).transform(lambda x: x/x.sum())
  
      weighting_links = network.links.loc[network.links.country!='DE', 'p_nom'].\
                  groupby(network.links.country).transform(lambda x: x/x.sum())
      network.lines["v_nom"] = network.lines.bus0.map(network.buses.v_nom)
      for country in cap_per_country:
  
          index_HV = network.lines[(network.lines.country == country) &(
                  network.lines.v_nom == 110)].index
          index_eHV = network.lines[(network.lines.country == country) &(
                  network.lines.v_nom > 110)].index
          index_links = network.links[network.links.country == country].index
  
          if not network.lines[network.lines.country == country].empty:
                  network.lines.loc[index_HV, 's_nom'] = weighting[index_HV] * \
                      cap_per_country[country] / capacity_factor['HV']
                      
                  network.lines.loc[index_eHV, 's_nom'] = \
                      weighting[index_eHV] * cap_per_country[country] /\
                                  capacity_factor['eHV']
  
          if not network.links[network.links.country == country].empty:
                  network.links.loc[index_links, 'p_nom'] = \
                                  weighting_links[index_links] * cap_per_country\
                                  [country] 
          if country == 'SE':
                  network.links.loc[network.links.country == country, 'p_nom'] =\
                  cap_per_country[country]
  
          if not network.lines[network.lines.country == (country+country)].empty:
              i_HV =  network.lines[(network.lines.v_nom == 110)&(
                      network.lines.country ==country+country)].index
              
              i_eHV =  network.lines[(network.lines.v_nom == 110)&(
                      network.lines.country ==country+country)].index
  
              network.lines.loc[i_HV, 's_nom'] = \
                                  weighting[i_HV] * cap_per_country[country]/\
                                  capacity_factor['HV']
              network.lines.loc[i_eHV, 's_nom'] = \
                                  weighting[i_eHV] * cap_per_country[country]/\
                                  capacity_factor['eHV']
  
          if not network.links[network.links.country == (country+country)].empty:
              i_links =  network.links[network.links.country ==
                                       (country+country)].index
              network.links.loc[i_links, 'p_nom'] = \
                  weighting_links[i_links] * cap_per_country\
                  [country]*capacity_factor