code: def inasafe_field_header(field, feature, parent):
      
      _ = feature, parent  # NOQA
      age_fields = [under_5_displaced_count_field, over_60_displaced_count_field]
      symbol_mapping = {
          'over': '>',
          'under': '<'
      }
  
      field_definition = definition(field, 'field_name')
      if field_definition:
          if field_definition in age_fields:
              header_format = tr('{symbol} {age} y.o')
              field_name = field_definition.get('field_name')
              if field_name:
                  symbol, age = field_name.split('_')[:2]
                  if symbol.lower() in list(symbol_mapping.keys()):
                      header_name = header_format.format(
                          symbol=symbol_mapping[symbol.lower()],
                          age=age
                      )
                      return header_name
  
          header_name = field_definition.get('header_name')
          name = field_definition.get('name')
          if header_name:
              return header_name.capitalize()
          else:
              return name.capitalize()
      return None
docs: Retrieve a header name of the field name from definitions.
  
      For instance:
      inasafe_field_header('minimum_needs__clean_water') -> 'Clean water'