'Returns HTML for a container, which will be populated later.
Args:
height: CSS string representing the height of the element, default
\'700px\'.
script: Visualization script contents, if the defaults are unacceptable.
init_message: Initial message to display.
Returns:
unicode with HTML contents.'

def initial_html(self, height='700px', script=None, init_message=None):

    if (script is None):
        script = _load_viz_script()
    if (init_message is None):
        init_message = 'Type    a    sentence    and    press    (enter)    to    see    the    trace.'
    (self.elt_id, div_html) = _container_div(height=height, contents='<strong>{}</strong>'.format(init_message))
    html = '\n                <meta    charset="utf-8"/>\n                {div_html}\n                <script    type=\'text/javascript\'>\n                {script}\n                </script>\n                '.format(script=script, div_html=div_html)
    return unicode(html, 'utf-8')
