def set_data_url(site_url, doc):
    """ Transform the image source.

    Note that all the images or resources have to be placed in the cube data
    folder.

    Parameters
    ----------
    site_url: str (mandatory)
        the server url.
    doc: str
        an html documentation.

    Returns
    -------
    doc: str
        the formatted html documentation.
    """

    # find specific tag for internal link
    doc = doc.replace("{siteURL}", site_url)
    return doc