Question

What is the reason of using float:left for an element with width:100% in the 1140px Grid V2 by Andy Taylor https://github.com/andytlr/cssgrid

.row .twelvecol {
    width: 100%;
    float: left;
}

Answer 1

If for no other reason, probably consistency. Since all the other column numbers have to be floated (to get them as column groups across the row), it may be simply so that the full width column .twelvecol would have the same float applied, therefore being less likely to cause issues of it behaving differently with its wrappers or content compared to other column groupings.

Look at this fiddle even in a modern browser (Firefox 18) and note how the second full width row (the third row of the example) is not showing its yellow background color because the float was removed from it but it holds a floated element in it. This would be the type of issue avoided by putting a float on it.