Leaving pixels behing for good:

The Frankengrid

Responsive twelve-column grid.

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Fluid-mode for mobile.

Markup is backward-compatible to the 1140 grid: see the 1140 rendered with the frankengrid

Fully em -based

Allows css-based zooming for different screen-resolutions while keeping layout.

Allows nesting!

Allows to work with a responsive (!) baseline-grid.

Mobile first.
CSS for mobile resources is delivered first to save bandwidth and requests. Resources for other resolutions are loaded via media-queries.

Nesting

hello world (this is a .twelvecol div)
.fourcol 01 (inside .eightcol )
.fourcol 02 (inside .eightcol ) (also needs last)
.fourcol 03 (next to .eightcol ) (also needs last)

This nesting of columns within columns is not possible with the 1140 due to its percentage-based columns.

That's the reason the Frankengrid exists.

Feedback is very welcome on github.