This page contains the issues that are not yet listed in the specification and the resolutions for issues that were in the spec. but got resolved.

Link to current Working Draft:http://www.w3.org/TR/css3-grid-layout/

Link to current Editor's draft: http://dev.w3.org/csswg/css3-grid-align/

Grid-layer vs. z-index property for Grid

Grid-layer is currently used to control the stacking of grid items in a grid element; one example of this that is mentioned in the current Editor's Draft would be using Grid to build a range control where the “thumb” of the control is displayed on top of the underlying track. However, grid-layer is in many ways similar to the existing z-index property. Is a separate property needed, or can z-index replace the grid-layer property?

We have three primary goals w/r/t stacking Grid Items:

1. Grid Items draw atomically. Like positioned elements, Grid has among its primary scenarios the ability to overlap and layer its items (see section 2.4 Grid Layering of Elements). To avoid a counter-intuitive interleaving of backgrounds, floats, and inline content, Grid Items should form a new stacking context.
2. Grid Items are in front of the Grid Element, even when the Grid Item is given a negative z-index. Imagine an author using a tool, right-clicking an item and choosing “send to back” from a context menu. The tool should set a negative z-index on the Grid Item and not have the Grid Item disappear behind the background of the Grid Element. Also, if a nested Grid is given a positive z-index, it should not cover its Grid Items. Therefore we need the Grid Element to serve as a stacking context for its Grid Items.
3. We want to avoid impacting any positioning scenarios. It would be unexpected if the author inadvertently changed the containing block or the stacking context for a positioned descendant just by inserting a Grid layout in its ancestry.

Z-index should be used to replace the grid-layer property (i.e. z-index applies to statically-positioned Grid Items.) Specifically, in cases where Grid Items overlap, z-index provides control over the drawing order of Grid Items. Both Grid elements and Grid Items generate a stacking context as described for floats (step 5, section 14) in the CSS3 Box Model.

Note also that using z-index in place of grid-layer has been previously discussed on the www-styling mailing list.

Fractional-track sizing algorithm update

The grid-sizing algorithm introduced in the previous Editor's Draft did not define the expected behavior for sizing a fractionally-sized track (e.g. 1fr, 2fr,…) when a Grid Element was shrink-to-fit. This should be addressed so that future implementations of Grid Layout behave predictably across platforms.

We propose to modify the existing grid sizing algorithm as follows: if the Grid Element is shrink-to-fit, then we set the size of a fractional track (i.e. determine the size of a '1fr' track) by making sure that 1) the proportions of all fractional tracks are preserved (e.g. a '1fr' track is half the size of a '2fr' track) and 2) fractional tracks are large enough contain all Grid Items that span them. If the Grid Element is not shrink-to-fit, then the algorithm follows its current path. The specific algorithm updates can be found in step 6 of the updated Editor's Draft.