bootstrap3-Grid System 网格系统
通过class="row"创建行，class="spanx"创建列?1.如何通过网格创建行与列2.添加响应式布局（自动与屏幕大小适应，对页面进行调整，以达到最佳显示效果）3.对列设置偏移量（偏移量也要与其它列一起计算总数不超过12列）4.网格嵌套（被嵌套的列数不能超过父列所占的列数）

?Following is a summary of what we have discussed in this tutorial:

Twitter Bootstrap's default grid sytem is 940px wide and can hold 12 columns.默认网格系统的配置：940px，网格分为12列In the Grid, rows are created with 'class="row"' and columns are created with 'class="spanx"', where x is a positive integer. Sum of x for all columns used must not exceed 12.通过class="row"创建行，class="spanx"创建列，所有列的x之和不能超过12By adding responsive css of Bootstrap, you can add responsive features to the deafult grid.可以添加响应式功能到默认网格系统中You can use offsets to create additional space to a column. For doing that 'class="offsetx"' is used, where x is a positive integer.if you are using offsets, then total number of columns, including number of offsets used, can not exceed 11.通过class="offsetx"可以为一列额外空出区域，总的列数（包括偏移列）不超过11？Columns can be nested. If nested columns are used, while counting total number of columns in the grid (in a row directly under container), nested columns are also counted with columns up in the hierarchy.列可以嵌套，在计算网格列总数时，被嵌套列也要一起计算，即遵守总列数<12的规定Offsetting can be performed on nested columns also.偏移属性同样可以使用在嵌套网格中??