How to use the postcss-values-parser.comma function in postcss-values-parser

parseInt(hex8.slice(2, 4), 16),
		parseInt(hex8.slice(4, 6), 16),
		parseInt(hex8.slice(6, 8), 16),
		Math.round(parseInt(hex8.slice(8, 10), 16) / 255 * alphaDecimalPrecision) / alphaDecimalPrecision
	];

	// return a new rgba function, preserving the whitespace of the original node
	const rgbaFunc = valueParser.func({ value: 'rgba', raws: Object.assign({}, node.raws) });

	rgbaFunc.append(valueParser.paren({ value: '(' }));
	rgbaFunc.append(valueParser.number({ value: r }));
	rgbaFunc.append(valueParser.comma({ value: ',' }));
	rgbaFunc.append(valueParser.number({ value: g }));
	rgbaFunc.append(valueParser.comma({ value: ',' }));
	rgbaFunc.append(valueParser.number({ value: b }));
	rgbaFunc.append(valueParser.comma({ value: ',' }));
	rgbaFunc.append(valueParser.number({ value: a }));
	rgbaFunc.append(valueParser.paren({ value: ')' }));

	return rgbaFunc;
};

node.value = 'rgb';

					// convert the lab gray lightness into rgb
					const [r, g, b] = lab2rgb(lightness, 0, 0).map(
						channel => Math.max(Math.min(Math.round(channel * 2.55), 255), 0)
					);

					// preserve the slash nodes within rgb()
					const openingSlash = node.first;
					const closingSlash = node.last;

					node.removeAll()
					// replace the contents of rgb with `(r,g,b`
					.append(openingSlash)
					.append(parser.number({ value: r }))
					.append(parser.comma({ value: ',' }))
					.append(parser.number({ value: g }))
					.append(parser.comma({ value: ',' }))
					.append(parser.number({ value: b }))

					// if an alpha channel was defined
					if (alpha < 1) {
						// rename the rgb() function to rgba()
						node.value += 'a';

						node
						// append the contents of rgba with `,a`
						.append(parser.comma({ value: ',' }))
						.append(parser.number({ value: alpha }));
					}

					// append the contents of rgb/rgba with `)`