Incorrect parsing on font-family with consecutive, leading, or trailing commas

[simon-paris]

Summary

Extra commas in font-family should cause errors. It parses them as an array containing empty strings ",," -> ["", "", ""], but unquoted empty strings aren't allowed.

e.g. Setting font-family to Arial, should fail, but actually results in Arial, (with a space inserted after each comma).

const el = document.createElement("input");
el.style.fontFamily = "Arial,";
expect(el.style.fontFamily).toBe(""); // actually: "Arial, "

More examples: ,Arial Arial, Arial,,Arial ,,

Expected

It should be an error. The result should be "".

Actual

It succeeds, and inserts a space after each comma.

Version

# pnpm why cssstyle
jsdom 28.1.0
└── cssstyle 6.0.1

Also affects 5.3.7.