The first excerpt is a horizontal dimension, the second is vertical, and the third is a content cell.
第一段是水平维度，第二段是竖直维度，第三段是内容单元格。
2
MDC automatically defines a cell (and creates blocks to store data for that cell) for each unique combination of MDC dimension values.
MDC则为每种惟一的mdc维值组合自动定义一个单元格(并创建块来存储那个单元格的数据)。
3
First we pick a random cell — or actually we pick one more than the cell itself in each dimension, since.shape gives us the length rather than the maximum index.