[css-grid-3][masonry] Make `item-tolerance` initial value `normal`

[ethanjv]

https://drafts.csswg.org/css-grid-3/#item-slack

With the latest resolution of using item-tolerance and making the item-* properties work differently in multiple layout types, it would make sense to change the initial value of this property to normal, following the similar behavior of [column|row]-gap.

Currently, only masonry has a use for item-tolerance, but it could potentially be reused elsewhere, while the normal behavior for masonry container can be kept as 1em for placement ties.

[Loirooriol]

I agree the initial value should be normal if the default behavior in masonry is 1em or something different than zero.

But normal can be superfluous if it ends up always behaving as 0px. So it may be better to settle #10882 first.

[css-meeting-bot]

The CSS Working Group just discussed [css-grid-3][masonry] Make `item-tolerance` initial value `normal` , and agreed to the following:

• RESOLVED: change initial value of item-tolerance to 'normal'

The full IRC log of that discussion

<alisonmaher> https://github.com//issues/10882
<JoshT> alisonmaher: two issues related to the issue
<JoshT> ... proposal to use 0 instead of 1em for initial value
<JoshT> ... may be less confusing for authors to see jumps
<JoshT> ... arguement against 0 is that it's not as accessible. less than 1px causes jumps in dom order
<JoshT> ... so proposed to keep 1em and see author feedback
<oriol> q+
<JoshT> ... column-gap has the same default
<JoshT> ... leave as 1em for now and use normal as initial value and compute to 1em
<astearns> ack oriol
<JoshT> oriol: agree that if we go for 0 for masonry, computed value should be normal
<JoshT> ... 1em for masonry and otherwise 0
<JoshT> ... preference still defaulting to 0 for masonry.
<astearns> q+
<JoshT> ... i agree 1em makes more sense. but preference is it may cause confusion
<JoshT> ... no one of the values in ???? does this
<astearns> s/????/masonry libraries/
<JoshT> ... providing a value that is small but not 0 may fail the expectations of authors
<JoshT> ... not sure if 1em will work well in general. something other than 0 may be good. 1em may be a random choice
<JoshT> ... have preference for 0 but not objecting to 1em. if we go for 0, may not need normal value
<JoshT> astearns: with the other issue about whether the default is 1em or 1lh, we can discuss separately for masonry. but making the default value 'normal' allows us to have that discussion for other layout modes that may need a different value
<astearns> ack astearns
<JoshT> oriol: masonry is strange if we say that the normal behaviour will be 0 because it will always be 0. but we can work out how to resolve this later
<astearns> ack fantasai
<JoshT> fantasai: I agree with oriol that it would be weird
<JoshT> ... but if we have a none 0 value, it should be normal.
<TabAtkins> +1
<JoshT> ... me and TabAtkins agree initial value should be 1em, to match row-gap
<JoshT> astearns: putting aside what it computes to, can we resolve that the initial value is 'normal' for now?
<JoshT> RESOLVED: change initial value of item-tolerance to 'normal'