Description
From https://www.w3.org/TR/css-color-4/#rgb-functions:
The final argument, the
<alpha-value>, specifies the alpha of the color. If given as a<number>, the useful range of the value is 0 (representing a fully transparent color) to 1 (representing a fully opaque color). If given as a<percentage>, 0% represents a fully transparent color, while 100% represents a fully opaque color. If omitted, it defaults to 100%.
Values outside these ranges are not invalid, but are clamped to the ranges defined here at computed-value time.
All user agents I've tested in fact do the clamping at parsing time:
<!doctype html>
<style>
#target {
color: rgba(400, 400, 300, -300);
}
</style>
<div id="target"></div>
<pre id="res"></pre>
<script>
res.innerText = "specified: " + document.styleSheets[0].cssRules[0].style.color + "\ncomputed: " + getComputedStyle(target).color;
</script>
Firefox, Safari and Chrome all give "specified: rgba(255, 255, 255, 0)"
Is there a disadvantage to just doing the clamping at parsing time? It is easier to implement and is already the behavior that we're living with.