The formatting model of CSS1 is changed to include the new properties. Elements can now specify that their content, including child elements, should be flowed into columns. That means that the width of those child elements is derived from the column width instead of the parent's full width. By default, i.e., when there is only one column, the sum of margin, border, padding and width for any block element is still equal to the width of the parent element. But when there are more columns, the sum is equal to the column width.
All columns have the same width.
The gutters and optional vertical rules between the columns can also be given. If the number of columns is specified, the actual column width is found by dividing the element's width by it. The actual width can thus be different from the desired width. All values, length or number, should only be used to determine the number of columns. Once found, the available space should be split into columns with equal widths and the same space between them.