docs: def writeCache(self, cachekey, content):
          """stores content in cache. 'cachekey' must be the same key as returned from checkCache().
          Returns the content."""
          self.rendercache[cachekey] = content
          try:
              open(cachekey, 'w').write(content)
          except:
              print("Error writing cache file", cachekey, ", will regenerate next time")
              traceback.print_exc()
          return content