[css-grid] Minor clarification to abstract

Author: fantasai

css-grid/Overview.bs

@@ -21,7 +21,7 @@ Editor: Rossen Atanassov, Microsoft, ratan@microsoft.com
 Former editor: Alex Mogilevsky, Microsoft Corporation, alexmog@microsoft.com
 Former editor: Phil Cupp, Microsoft Corporation, pcupp@microsoft.com
 Issue Tracking: Disposition of Comments http://dev.w3.org/csswg/css-grid-1/issues
-Abstract: This CSS module defines a two-dimensional grid-based layout system, optimized for user interface design. In the grid layout model, the children of a grid container can be positioned into arbitrary slots in a flexible or fixed predefined layout grid.
+Abstract: This CSS module defines a two-dimensional grid-based layout system, optimized for user interface design. In the grid layout model, the children of a grid container can be positioned into arbitrary slots in a predefined flexible or fixed-size layout grid.
 Ignored Terms: containing block, <positive-integer>, <ident>, auto, grid-*-start, grid-*-end, flex factor, flex factors, block formatting context, grid-auto-position, min size property, max size property
 Link Defaults: css21 (property) margin/min-height/max-height/min-width/max-width, css-align-3 (dfn) alignment container/alignment subject/box alignment properties, css-align-3 (value) stretch/baseline, css-position-3 (property) left, css-position-3 (property) position, css-writing-modes-3 (dfn) start/end
 At Risk: the ''grid-template-rows/subgrid'' value of 'grid-template-columns' and 'grid-template-rows', and its component parts individually