Fix html generation errors for boolean options. Code was generating xhtml form for html4 output. In xhtml, Boolean attributes like 'disabled', 'required' are represented with a value that is the same as the attribute name. E.G. <input required="required" ...>. Html 5 (and 4) represents the same as <input required ...> . Recognize booleans in one of two ways: value is None value is the same as the attribute name Make html4 and xhtml variants of cgi_escape_attrs. Have input_htmlp4 and input_xhtml call the proper variant. Also set HTMLInputMixin property cgi_escape_atrs to select proper one similar to self.input definition. Then replace calls to cgi_escape_attr with self.cgi_escape_attrs to get correct output.

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