[css-animations] Clarify whether `<keyframes-name>` supports the empty string

[yisibl]

The spec allows <string> here #118 (comment), but does not further clarify whether empty strings("" or " ") are allowed.

@ewilligers Says:

Also, do we want to ban the empty string '""' ?
#2435 (comment)

• From the CSS author's point of view, empty strings seem to be meaningless.
• For current implementations across browsers, this has significant compatibility issues.

@keyframes "" {}

If the browser supports it, the page background color will be green.

@-webkit-keyframes "" {
    to {
        background: green
    }
}

@-moz-keyframes "" {
    to {
        background: green
    }
}

body {
    background: red;
    -webkit-animation: "" 0s ease 1 forwards;
    -moz-animation: "" 0s ease 1 forwards;
}

• -webkit- (Chrome) ✅
• -webkit-(Safari) ❌
• -moz-(Firefox) ❌
• without prefix(both) ❌ Firefox bug

@keyframes " " {}

@-webkit-keyframes " " {
    to {
        background: green
    }
}

@-moz-keyframes " " {
    to {
        background: green
    }
}

body {
    background: red;
    -webkit-animation: " " 0s ease 1 forwards;
    -moz-animation: " " 0s ease 1 forwards;
}

• -webkit- (Chrome) ✅
• -webkit-(Safari) ✅
• -moz-(Firefox) ✅

[yisibl]

Firefox has a bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1554737

[tabatkins]

I'm inclined to say that empty string is not allowed, as that cannot be reproduced as an ident. (All other strings can be, with suitable escapes.)

[fantasai]

I agree with @tabatkins

[javifernandez]

@fantasai is the PR #12985 enough to solve this issue ?