[css-link-params] `url(param())` vs. `src(string())`

[Crissov]

The specification introduces the param() function from the link-parameters property also inside url() as a modifier because the URL inside that cannot be altered to contain a parameter fragment identifier. However, with src() and string() from #542, this would be possible.

:root {
--primary-color: green;
}
.property {
  background-image: url("image.svg");
  link-parameters: param(--color, var(--primary-color));
}
.fragment { /* static */
  background-image: url("image.svg#param(--color, green)");
}
.url {
  background-image: url("image.svg"
    param(--color, var(--primary-color))
  );
}
.src {
  background-image: src(string("image.svg#param(--color," var(--primary-color) ")"
  );
}

Do we really need all those different ways? Should string concatenation replace the URL modifier variant in 2.3?

I also don’t quite see why a special function, i.e. param(), would be required for the property variant in 2.1. link-parameter (should be singular) could just take a comma separated list of pairs of a dashed ident and a value. That value cannot contain a comma itself anyway.

[tabatkins]

It is possible to do it with string concatenation, yes, but string concatenation is a lot clumsier than using normal CSS syntax at the CSS token level.

The URL modifier syntax isn't designed for use inside of CSS, but rather to make it possible to pass these values directly in <img src>.