docs: function parseBoolean( str, options ) {
  	var opts = {};
  	var err;
  	if ( arguments.length > 1 ) {
  		err = validate( opts, options );
  		if ( err ) {
  			return err;
  		}
  	}
  	if ( opts.strict ) {
  		if ( str === 'true' ) {
  			return true;
  		}
  		if ( str === 'false' ) {
  			return false;
  		}
  	} else {
  		str = str.toLowerCase();
  		if (
  			str === 'true' ||
  			str === 't'
  		) {
  			return true;
  		}
  		if (
  			str === 'false' ||
  			str === 'f'
  		) {
  			return false;
  		}
  	}
  	return new TypeError( 'invalid value. Unable to parse string as a boolean. Value: `' + str + '`.' );
  }