function render( format ) {
	/* eslint-disable no-invalid-this */
	var out;

	debug( 'Render format: %s.', format );

	debug( 'Rendering...' );
	if ( this._engine === 'svg' ) {
		out = renderSVG( this );

		// Default render format is virtual DOM...
		if ( format === 'html' ) {
			out = vdom2html( out );
		}
		this.emit( 'render', out );
	}
	return out;
}
Renders a histogram.

@private
@param {string} format - render format
@returns {(VTree|string)} virtual tree or a string