function set( label ) {
	/* eslint-disable no-invalid-this */
	if ( !isString( label ) ) {
		throw new TypeError( format( 'invalid assignment. `%s` must be a string. Value: `%s`.', 'label', label ) );
	}
	debug( 'Current value: %d.', this._label );

	this._label = label;
	debug( 'New Value: %d.', this._label );

	this.emit( 'change' );
}
Sets the path label.

@private
@param {string} label - label
@throws {TypeError} must be a string