That only works with Sigil, Calibre, Chrome and other Webkit-based apps.
For EPUB 3 the correct way is to use the CSS 3 properties column-count, column-width, etc.
Also you can use either column-count or column-width, the first one if you want a fixed number of columns no matter the size of the screen/window and the second one (without column-count) if you want the number to vary and fit the width of the screen, but its value should be in em or ex rather than %. The second one is better if you want your epub to remain readable on small readers