Please allow percentage values for column-gap. An example use case would be:

.article {
  column-count: 3; /* each 30% */
  column-gap: 5%;
}

'Percentages' would be from the calculated width of the containing block.

Links

• https://drafts.csswg.org/css-multicol-1/#column-gap
• https://lists.w3.org/Archives/Public/www-style/2013Feb/0494.html
• https://lists.w3.org/Archives/Public/www-style/2013Feb/0572.html

As I understand it, percentages are not allowed on column-width because using column-count is preferred for a fluid layout. This makes sense, and I agree, but it sounds like a case of "we're disallowing this feature because it's bad practice." I'm not sure how that fits into CSSWG principles. Furthermore, column-width still allows vw units, which can be used to achieve (approximately) the same effect as percentages.