[css-grid-2] Fix up references to implicitly named lines. w3c#5393

Author: fantasai

css-grid-2/Overview.bs

@@ -218,14 +218,14 @@ Characteristics of a Subgrid Item</h3>
 
 			Note: If a <a>named grid area</a>
 			only partially overlaps the <a>subgrid</a>,
-			its <a lt="implicit named lines">implicit names</a>
+			its [=implicitly-created line names=]
 			will be assigned
 			to the first and/or last line of the <a>subgrid</a>
 			such that a <a>named grid area</a> exists
 			representing that partially overlapped area of the <a>subgrid</a>;
-			thus the <a>implicit named lines</a> of the <a>subgrid</a>
+			thus the [=line name=] assignments of the <a>subgrid</a>
 			might not always correspond exactly
-			to the <a>implicit named lines</a> of the parent <a>grid</a>.
+			to the [=line name=] assignments of the parent <a>grid</a>.
 
 			These names are also in <em>addition</em> to
 			any line names specified locally on the subgrid.