'Register extension instances.'

def extendMarkdown(self, md, md_globals):

    md.registerExtensions(extensions, self.config)
    if (not md.safeMode):
        md.preprocessors[u'html_block'].markdown_in_raw = True
        md.parser.blockprocessors.add(u'markdown_block', MarkdownInHtmlProcessor(md.parser), u'_begin')
        md.parser.blockprocessors.tag_counter = (-1)
        md.parser.blockprocessors.contain_span_tags = re.compile(u'^(p|h[1-6]|li|dd|dt|td|th|legend|address)$', re.IGNORECASE)
