There is discussion in 2013, raised by @tabatkins regarding column widths of 0. See column-width bound (>0) is illegal

Yeah, we've pretty strictly applied the "no open ranges" rule, except when compat restricts us (like in transform-origin). I think the right answer here is obvious - allow zero, require UAs to clamp to a UA-specific minimum value, suggested to be 1px.

I just came across this inconsistency while testing column-width animation, and was about to create an issue recommending that we accept any non-negative value, when I search and found that this issue had already been raised.

They seem likely to lead to interoperability problems

It has (Test):

Firefox accepts 0px and 0em as specified values for column-width. Other browsers reject these values.

Edge never gives 0px as a computed value of column-width (e.g. as the result of a calc expression, or when font-size is 0px), instead it gives a fraction of a pixel. Other browsers can give 0px as a computed value of column-width.

As Chrome and Safari can give 0px as a computed value, but don't accept 0px as a specified value, they don't round-trip.

Allowing column-width:0 makes sense, but if column-gap is also 0 at the same time, we'll end up with an infinite used column-count, and there'll be no progression in the inline direction. Apart from that, the only interesting implication of infinite column-count that I can think of, spec-wise, is column balancing:

<div id="mc" style="column-width:0; column-gap:0;">
  <div style="height:10000px;"></div>
</div>

With auto height and column balancing and an infinite number of columns, we'll end up with a silly height of #mc. We have 10000px to distribute over ∞ columns, so even a height of 0 would do in that sense, except that then we'd have no block progression, and luckily a fragmentainer is required to be >= 1px tall [1]. So we'll "only" end up with 10000 columns?

[1] https://www.w3.org/TR/css-break-3/#breaking-rules

The Working Group just discussed Contradictions about whether zero is allowed for 'column-width', and agreed to the following resolutions:

• RESOLVED: We allow 0 for column-width for the purpose of parsing, 1px is the minimum clamping value used for anything after parsing

I tend to think that for animation, the clamping should be at used value time rather than computed value time.

So in terms of wording for the spec. The current wording for computed value is correct "the absolute length, zero or larger"?

And this new wording should replace, "Specified values must be greater than 0" with something like:

"Specified values of 0 are allowed, however the used value of any value less than 1px will be clamped at 1px."

"Specified values of 0 are allowed, however the used value of any value less than 1px will be clamped at 1px."

It needs to be clear if specified values may be negative (no) or between 0 and 1 (yes).

We could have the common wording "Negative values are not allowed." and "the absolute length" instead of having unusual wording for the specified and computed values. And add "Used values will be clamped to a minimum of 1px."