{"ast_node_type":"variable","tokens":[{"end":68,"kind":"keyword","start":0,"text":"let"}]}
            let line = line.as_deref().map_err(|e| anyhow!("{e}"))?;
                .ok_or_else(|| anyhow!("target block for the title is not found"))?;
            if line.starts_with(IMAGE_BLOCK_PREFIX) {