def textmark(string, mark=""):
    """
    Excerpt of content

        >>> textmark('<p>Hello</p><!----><p>World</p>')
        '<p>Hello</p>'
        >>> textmark('<p>Hello</p><!--ex--><p>World</p>', 'ex')
        '<p>Hello</p>'
        >>> textmark('<p>Hello</p><!----><p>World</p><!--test-->', 'test')
        '<p>Hello</p><!----><p>World</p>'
    """
    mark = "<!--{0}-->".format(mark)
    if mark in string:
        index = string.index(mark)
        return string[0:index]
    return ""