public static function purify($keywords){

		$keywords	= filter_var($keywords, FILTER_SANITIZE_STRING,
			FILTER_FLAG_NO_ENCODE_QUOTES);
		$keywords	= preg_replace('/\s\s+/', ' ', $keywords);
		$keywords	= trim($keywords);

		$dirty_tokens = explode(' ', $keywords);
		$clean_tokens = [];

		foreach($dirty_tokens as $token){

			// Check whether a string has at least 3 alphanumeric characters
			$pattern = "/[\w'\"`-]{3,}/i";
			if(preg_match($pattern, $token)){

				if(strlen($token) < 64){

					$clean_tokens[] = $token;
				}
			}
		}

		return [
			'dirty' => $dirty_tokens,
			'clean' => $clean_tokens,
			'stems' => $clean_tokens
		];
	}