def get_caption_comments(content):
    """Retrieve an id and a caption from a code cell.

    If the code cell content begins with a commented
    block that looks like

    ## fig:id
    # multi-line or single-line
    # caption

    then the 'fig:id' and the caption will be returned.
    The '#' are stripped.
    """

    if not content.startswith('## fig:'):
        return None, None

    content = content.splitlines()

    id = content[0].strip('## ')

    caption = []
    for line in content[1:]:
        if not line.startswith('# ') or line.startswith('##'):
            break
        else:
            caption.append(line.lstrip('# ').rstrip())

    # add " around the caption. TODO: consider doing this upstream
    # in pandoc-attributes
    caption = '"' + ' '.join(caption) + '"'
    return id, caption
Retrieve an id and a caption from a code cell.

    If the code cell content begins with a commented
    block that looks like

    ## fig:id
    # multi-line or single-line
    # caption

    then the 'fig:id' and the caption will be returned.
    The '#' are stripped.