Specs:

• https://drafts.csswg.org/css-align/#valdef-row-gap-normal

  The normal represents a UA-dependent length on multi-column elements, and computes to 0px in all other contexts.

• https://drafts.csswg.org/css-multicol-1/#valdef-column-gap-normal

  Identical to , but with a UA-specified length. A value of 1em is suggested.

There's an issue in css-align about this:

ISSUE 4: Should normal just compute to 1em in multicol?

I've realized there's a WPT test checking exactly that: http://w3c-test.org/css/css-multicol/multicol-gap-001.xht
Right now is marked as optional, but it passes in all the browsers I checked: Chromium, Safari, Firefox and Edge.

Maybe it's possible to update the specs and make this test mandatory. WDYT?