A single column in a {@link Columns} element. Each child of the{@link Column} element is placed in each successive cell of the grid. Thecolumn with the most child elements determines the number of rows in each column.
The use of column is mainly to define attributes for each cell in the grid.
Default {@link #getZclass}: z-column. (since 3.5.0)
@author tomyeh
@since 3.5.2