[css-grid-2] Add back subgrid-local line names (which we had elided for simplicity of discussion over per-axis vs dual-axis proposals). w3c#2280 w3c#2622

Author: fantasai

css-grid-2/Overview.bs

@@ -92,19 +92,44 @@ Establishing a Subgrid: Per-Axis Proposal</h3>
 
 	<pre class="propdef">
 	Name: grid-template-rows, grid-template-columns
-	New values: subgrid
+	New values: subgrid <<line-name-list>>?
 	</pre>
 
 	<dl dfn-for="grid-template-rows, grid-template-columns" dfn-type=value>
-		<dt><dfn>subgrid</dfn>
+		<dt><dfn id="subgrid-listing">subgrid <<line-name-list>>?</dfn>
 		<dd>
-			Tracks are <a>subgridded</a> in this axis:
-			the tracks are adopted from the the parent grid tracks that it spans.
-			If there is no parent grid, equivalent to
+			The <dfn value for="grid-template-rows, grid-template-columns">subgrid</dfn> value
+			indicates that the grid will adopt the spanned portion of its parent grid in that axis.
+			Rather than being specified explicitly,
+			the sizes of the grid rows/columns
+			will be taken from the parent grid's definition.
+
+			The <<line-name-list>> argument allows local naming of the grid lines propagated from the parent grid:
+			if a <<line-name-list>> is given,
+			the specified <<line-names>>s are assigned to the subgrid’s <a>explicit grid lines</a>,
+			one per line, starting with line 1.
+			Excess <<line-names>> are ignored.
+
+			If there is no parent grid,
+			this value is equivalent to
 			the initial value, ''grid-template-rows/none''.
 	</dl>
 
-	Issue: Add back syntax for overlaying line names.
+	The syntax of <<line-name-list>> is defined as follows:
+
+	<pre class="prod">
+		<dfn>&lt;line-name-list></dfn> = [ <<line-names>> | <<name-repeat>> ]+
+		<dfn>&lt;line-names></dfn>     = '[' <<custom-ident>>* ']'
+		<dfn>&lt;name-repeat></dfn>    = repeat( [ <positive-integer> | auto-fill ], <line-names>+)
+	</pre>
+
+	The <<name-repeat>> variant of the ''repeat()'' notation
+	<!-- is for adding line names to <a href="#subgrids">subgrids</a> and -->
+	can only be used with the ''grid-template-rows/subgrid'' keyword:
+	it only repeats names.
+	The ''auto-fill'' keyword is only valid once per <<line-name-list>>,
+	and repeats enough times for the name list to match the subgrid’s specified <a>grid span</a>
+	(falling back to 0 if the span is already fulfilled).
 
 <h3 id="subgrid-items">
 Characteristics of a Subgrid Item</h3>
@@ -116,6 +141,7 @@ Characteristics of a Subgrid Item</h3>
 			The number of explicit tracks in each subgridded dimension
 			is given by its <a>grid span</a> in that dimension,
 			rather than by 'grid-template-rows'/'grid-template-columns'.
+			The track sizes are governed by the parent grid.
 
 		<li>
 			The <a>grid-placement properties</a> of the <a>subgrid</a>’s <a>grid items</a>
@@ -128,6 +154,11 @@ Characteristics of a Subgrid Item</h3>
 			the subgridded lines
 			automatically receive the line names specified on the parent <a>grid</a>.
 
+			ISSUE: If a <<line-name-list>> is provided,
+			should this hide the names received from the parent
+			or be in addition to those names?
+			(<a href="https://github.com/w3c/csswg-drafts/issues/2622">Issue 2622</a>)
+
 		<li>
 			The <a>subgrid</a> itself lays out as an ordinary <a>grid item</a> in its parent grid,
 			but acts as if it was completely empty for sizing purposes