[css-box-3] Defer margin-trim to L4 per https://lists.w3.org/Archives/Public/www-style/2020Feb/0011.html

Author: fantasai

css-box-3/Overview.bs

@@ -8,7 +8,7 @@ Group: csswg
 ED: https://drafts.csswg.org/css-box-3/
 TR: https://www.w3.org/TR/css-box-3/
 Previous Version: https://www.w3.org/TR/2018/WD-css-box-3-20180802/
-Abstract: This specification describes the margin and padding properties, which create spacing in and around a CSS box. It may later be extended to include borders (currently described in [[css-backgrounds-3]]).
+Abstract: This specification describes the margin and padding properties, which create spacing in and around a CSS box.
 Editor: Elika J. Etemad / fantasai, Invited Expert, http://fantasai.inkedblade.net/contact, w3cid 35400
 Ignored Terms: internal table elements, block layout
 </pre>
@@ -349,96 +349,6 @@ Margin Shorthand: the 'margin' property {#margin-shorthand}
 		</pre>
 	</div>
 
-Margins at Container Edges: the 'margin-trim' property {#margin-trim}
---------------------------
-
-	<pre class="propdef">
-		Name: margin-trim
-		Value: none | in-flow | all
-		Initial: none
-		Applies to: [=block containers=], [=multi-column containers=]
-		Inherited: no
-		Percentages: N/A
-		Computed value: keyword as specified
-		Animation type: discrete
-	</pre>
-
-	Oftentimes, margins are desired between siblings,
-	but not at the start/end of the container
-	where spacing can be controlled with padding.
-	This property allows the container
-	to trim the margins of its children
-	where they adjoin the container’s edges.
-	Values have the following meanings:
-
-	<dl dfn-type=value dfn-for=margin-trim>
-		<dt><dfn>none</dfn>
-		<dd>
-			Margins are not trimmed by the container.
-
-			Note: However, in block layout,
-			child margins can collapse with their parent.
-			See <a href="https://www.w3.org/TR/CSS2/box.html#collapsing-margins">CSS2&sect;8.3.1: Collapsing Margins</a>.
-
-		<dt><dfn>in-flow</dfn>
-		<dd>
-			For in-flow boxes contained by this box,
-			block-axis margins adjacent to the box’s edges
-			are truncated to zero.
-			It also truncates any margins collapsed with such a margin.
-
-		<dt><dfn>all</dfn>
-		<dd>
-			Trims the margins of in-flow boxes as for ''in-flow'',
-			but also trims any float margin
-			whose [=margin edge=] coincides
-			with the container’s [=content edge=].
-	</dl>
-
-	Specifically, for [=block containers=],
-	''margin-trim: in-flow'' or ''margin-trim: all'' discards:
-	<ul>
-		<li>The block-start margin of a block-level first child.
-		<li>The block-end margin of a block-level last child.
-		<li>Any margin collapsed with these margins.
-	</ul>
-
-	''margin-trim: all'' also affects floats
-	for which the [=block container=] is a [=containing block=] by:
-	<ul>
-		<li>
-			Discarding the [=block-start=] [=margin=] of any float
-			whose [=block-start=] [=outer edge=] coincides
-			with the [=block-start=] [=inner edge=] of the container.
-		<li>
-			Discarding the [=inline-start=]/[=inline-end=] [=margin=]
-			of an [=inline-start=]/[=inline-end=] float (or equivalent)
-			whose [=outer edge=] on that side coincides
-			with the [=inner edge=] of the container.
-		<li>
-			Zeroing the [=inline-axis=] margins of a float
-			for the purpose of calculating its [=intrinsic size contributions=]
-			or its [=size=] in the container’s [=inline axis=].
-		<li>
-			Trimming the [=block-end=] margins of a float
-			to the extent necessary to prevent such a margin
-			from extending the [=block size=]
-			of a [=block formatting context root=].
-	</ul>
-
-	ISSUE: Should this property apply to [=flex containers=] or [=grid containers=]?
-
-	ISSUE: Should floats have a <css>floats</css> value that only affects floats?
-
-	Note: See also the 'margin-break' property,
-	which applies to the box’s own margins
-	when they adjoin a <a>fragmentation break</a>
-	(page break / column break / etc.).
-
-	ISSUE: Define how this property affects margins at breaks
-	if the box establishes a <a>fragmentation context</a>.
-	See also <a href="https://github.com/w3c/csswg-drafts/issues/3314">Issue 3314</a>.
-
 Padding {#paddings}
 =======
 
@@ -551,7 +461,6 @@ Changes Since CSS Level 2 {#changes}
 	The following changes have been made to this module
 	since <a href="https://www.w3.org/TR/CSS2/box.html">CSS Level 2</a>:
 	<ul>
-		<li>Adding the 'margin-trim' property.
 		<li>Adapting the prose slightly to account for vertical <a>writing modes</a>.
 	</ul>