def env(cls, separator=None, match=None, whitelist=None, parse_values=None, to_lower=None, convert_underscores=None):
        """Set environment variables as a source.

        By default all environment variables available to the process are used.
        This can be narrowed by the args.

        Args:
            separator: Keys are split along this character, the resulting
                splits are considered nested values.
            match: Regular expression for key matching. Keys matching the
                expression are considered whitelisted.
            whitelist: Only use environment variables that are listed in this
                list.
            parse_values: Try to parse all variable for well-known types.
            to_lower: Convert all variable names to lower case.
            convert_underscores: Convert all underscores in the name to dashes,
                this takes place after separation via the separator option.
        """
        cls.__hierarchy.append(env.Env(separator, match, whitelist, parse_values, to_lower, convert_underscores))
Set environment variables as a source.

        By default all environment variables available to the process are used.
        This can be narrowed by the args.

        Args:
            separator: Keys are split along this character, the resulting
                splits are considered nested values.
            match: Regular expression for key matching. Keys matching the
                expression are considered whitelisted.
            whitelist: Only use environment variables that are listed in this
                list.
            parse_values: Try to parse all variable for well-known types.
            to_lower: Convert all variable names to lower case.
            convert_underscores: Convert all underscores in the name to dashes,
                this takes place after separation via the separator option.