Function to_markdown_node 

pub fn to_markdown_node<S: AsRef<str>>(
    document: &Document<S>,
    node: NodeId,
    options: &Options,
) -> Result<String, Message>

Serialize a document subtree with formatting options.

The output always uses LF line endings. Non-empty block subtrees end with a line ending; inline (phrasing) subtrees, such as text, emphasis, or a link, are returned without an added line ending.

Errors

Returns an invalid node index, invalid formatting options, unsupported syntax metadata, or unsupported content shapes.