Template:Multi-column TOC/doc

Supports widths of 20em, 25em (default), and 30em, maximum number of columns of 2 (default), 3, and 4.

Usage
Add to make the table of contents have a max of 3 columns with a minimum width of 20em. Uses WP:TemplateStyles, so it styles the table of contents wherever it is, and does not determine the position of the table of contents.