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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def serve_doc(app, url):
 """ Serve API documentation extracted from request handler docstrings Parameters: * app: Grole application object * url: URL to serve at """

    @app.route(url, doc=False)
    def index(env, req):
        ret = ''
        for d in env['doc']:
            ret += 'URL: {url}, supported methods: {methods}{doc}\n'.format(**d)
        return ret