Bootstrap v4.0.0-alpha.3 发布了，该版本主要对网格系统做了如下改进：
Our ready-made grid classes (containers and columns) are now behind a Sass variable, meaning grid classes can easily be disabled via Sass variable. Update the boolean
$enable-grid-classes variable and recompile to remove them.
Grid modifier classes are simpler and no longer require the
col- prefix. For example, instead of
.col-pull-*-*, we now have
Mixins have been changed, and then changed
again, to in an effort to keep generated classes simple and cooperative
between standard and flexbox modes. Our two primary column mixins are
make-col-ready, which houses the
min-height (to prevent collapsing empty columns), and
make-col for setting the
Added a grid customization section to the docs to explain how to change the number of columns, grid tier breakpoints, container widths, and more.