The patch for bug 119540 will add parsing support for named grid lines. That's the first step, after that we need to use that information to properly position the different elements in the grid.
This was done in Blink in:
Properly resolve named grid lines
This change adds the code to convert from a raw named grid line
(stored in RenderStyle) to its actual grid position.
[CSS Grid Layout] Support named grid lines with 'span'
This change implements the resolution for named grid lines with 'span',
which is the missing piece to fully support named grid lines.
Created attachment 210471 [details]
Comment on attachment 210471 [details]
Clearing flags on attachment: 210471
Committed r155181: <http://trac.webkit.org/changeset/155181>
All reviewed patches have been landed. Closing bug.