function set( orientation ) {
	/* eslint-disable no-invalid-this */
	if ( indexOf( ORIENTATIONS, orientation ) === -1 ) {
		throw new TypeError( format( 'invalid assignment. `%s` must be one of the following: "%s". Value: `%s`.', 'xAxisOrient', ORIENTATIONS.join( '", "' ), orientation ) );
	}
	if ( orientation !== this._xAxisOrient ) {
		debug( 'Current value: %s.', this._xAxisOrient );

		this._xAxisOrient = orientation;
		debug( 'New value: %s.', this._xAxisOrient );

		this.emit( 'change' );
	}
}
Sets the x-axis orientation.

@private
@param {string} orientation - axis orientation
@throws {TypeError} must be either `'bottom'` or `'top'`