possible bug

Hello.

I validated an HTML doc with some styles and the validator found the error:
background: hsl(0 70 50):  CSS: background: 70 is not a valid HSL color.

The error can be fixed if I use background hsl(0 70% 50%) instead, but according to https://drafts.csswg.org/css-color-4/#the-hsl-notation
the syntax hsl(0 70 50) should be valid.

Please find:<modern-hsl-syntax> = hsl(
    [<hue> | none]
    [<percentage> | <number> | none]
    [<percentage> | <number> | none]
    [ / [<alpha-value> | none] ]? )
.... The next two arguments are the saturation and lightness, respectively.
For saturation, 100% or 100 is a fully-saturated, bright color,
and 0% or 0 is a fully-unsaturated gray. For lightness, 50% or 50 represents the "normal" color,
while 100% or 100 is white and 0% or 0 is black.

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