code: def detect_fold_level(self, prev_block, block):
          
          text = block.text()
          prev_lvl = TextBlockHelper().get_fold_lvl(prev_block)
          # round down to previous indentation guide to ensure contiguous block
          # fold level evolution.
          indent_len = 0
          if (prev_lvl and prev_block is not None and
             not self.editor.is_comment(prev_block)):
              # ignore commented lines (could have arbitary indentation)
              prev_text = prev_block.text()
              indent_len = (len(prev_text) - len(prev_text.lstrip())) // prev_lvl
          if indent_len == 0:
              indent_len = len(self.editor.indent_chars)
  
          return (len(text) - len(text.lstrip())) // indent_len
docs: Detects fold level by looking at the block indentation.
  
          :param prev_block: previous text block
          :param block: current block to highlight