code: def _prepare_app(self, app):
          
  
          # Ensure these keys' values are lists
          for key in ['url', 'html', 'script', 'implies']:
              try:
                  value = app[key]
              except KeyError:
                  app[key] = []
              else:
                  if not isinstance(value, list):
                      app[key] = [value]
  
          # Ensure these keys exist
          for key in ['headers', 'meta']:
              try:
                  value = app[key]
              except KeyError:
                  app[key] = {}
  
          # Ensure the 'meta' key is a dict
          obj = app['meta']
          if not isinstance(obj, dict):
              app['meta'] = {'generator': obj}
  
          # Ensure keys are lowercase
          for key in ['headers', 'meta']:
              obj = app[key]
              app[key] = {k.lower(): v for k, v in obj.items()}
  
          # Prepare regular expression patterns
          for key in ['url', 'html', 'script']:
              app[key] = [self._prepare_pattern(pattern) for pattern in app[key]]
  
          for key in ['headers', 'meta']:
              obj = app[key]
              for name, pattern in obj.items():
                  obj[name] = self._prepare_pattern(obj[name])
docs: Normalize app data, preparing it for the detection phase.