docs: def _braket_fmt(self, expr_type):
          """Return a format string for printing an `expr_type`
          ket/bra/ketbra/braket"""
          mapping = {
              True: {  # use braket package
                  'bra': {
                      True: r'\Bra{{{label}}}^{{({space})}}',
                      'subscript': r'\Bra{{{label}}}_{{({space})}}',
                      False:  r'\Bra{{{label}}}'},
                  'ket': {
                      True: r'\Ket{{{label}}}^{{({space})}}',
                      'subscript': r'\Ket{{{label}}}_{{({space})}}',
                      False:  r'\Ket{{{label}}}'},
                  'ketbra': {
                      True:
                          r'\Ket{{{label_i}}}\!\Bra{{{label_j}}}^{{({space})}}',
                      'subscript':
                          r'\Ket{{{label_i}}}\!\Bra{{{label_j}}}_{{({space})}}',
                      False: r'\Ket{{{label_i}}}\!\Bra{{{label_j}}}'},
                  'braket': {
                      True: r'\Braket{{{label_i} | {label_j}}}^({space})',
                      'subscript': r'\Braket{{{label_i} | {label_j}}}_({space})',
                      False:  r'\Braket{{{label_i} | {label_j}}}'}},
              False: {  # explicit tex macros
                  'bra': {
                      True:
                          r'\left\langle {label} \right\rvert^{{({space})}}',
                      'subscript':
                          r'\left\langle {label} \right\rvert^{{({space})}}',
                      False:
                          r'\left\langle {label} \right\rvert'},
                  'ket': {
                      True:
                          r'\left\lvert {label} \right\rangle^{{({space})}}',
                      'subscript':
                          r'\left\lvert {label} \right\rangle_{{({space})}}',
                      False:  r'\left\lvert {label} \right\rangle'},
                  'ketbra': {
                      True:
                          r'\left\lvert {label_i} \middle\rangle\!'
                          r'\middle\langle {label_j} \right\rvert^{{({space})}}',
                      'subscript':
                          r'\left\lvert {label_i} \middle\rangle\!'
                          r'\middle\langle {label_j} \right\rvert_{{({space})}}',
                      False:
                          r'\left\lvert {label_i} \middle\rangle\!'
                          r'\middle\langle {label_j} \right\rvert'},
                  'braket': {
                      True:
                          r'\left\langle {label_i} \middle\vert '
                          r'{label_j} \right\rangle^{{({space})}}',
                      'subscript':
                          r'\left\langle {label_i} \middle\vert '
                          r'{label_j} \right\rangle_{{({space})}}',
                      False:
                          r'\left\langle {label_i} \middle\vert '
                          r'{label_j} \right\rangle'}}
              }
          hs_setting = bool(self._settings['show_hs_label'])
          if self._settings['show_hs_label'] == 'subscript':
              hs_setting = 'subscript'
          return mapping[self._settings['tex_use_braket']][expr_type][hs_setting]