docs: def detect_fold_level(self, prev_block, block):
          """
          Detects fold level by looking at the block indentation.
  
          :param prev_block: previous text block
          :param block: current block to highlight
          """
          text = block.text()
          # round down to previous indentation guide to ensure contiguous block
          # fold level evolution.
          return (len(text) - len(text.lstrip())) // self.editor.tab_length