docs: def convert_compound_entry(self, compound):
          """Convert compound entry to YAML dict."""
          d = OrderedDict()
          d['id'] = compound.id
  
          order = {
              key: i for i, key in enumerate(
                  ['name', 'formula', 'formula_neutral', 'charge', 'kegg',
                   'cas'])}
          prop_keys = (
              set(compound.properties) - {'boundary', 'compartment'})
          for prop in sorted(prop_keys,
                             key=lambda x: (order.get(x, 1000), x)):
              if compound.properties[prop] is not None:
                  d[prop] = compound.properties[prop]
  
          return d