docs: def interpret(self, msg):
          """ Load input """
          slides = msg.get('slides', [])
          self.cache = msg.get('folder')
          self.gallery = msg.get('gallery', '..')
  
          with open(self.cache + '/slides.txt', 'w') as logfile:
              for ix, item in enumerate(slides):
                  image = self.prepare_image(item)
                  filename = self.cache_image(item, image)
  
                  text = item.get('caption', '')
  
                  # do not write text for heading images
                  if item.get('heading'):
                      text = ''
                      
                  if text:
                      with open(filename + '.txt', 'w') as caption:
                          caption.write(text)
                  print('%s,%d' % (filename, item.get('time', 0)), file=logfile)