Multi checkbox field- multi column layout?

[Will Wilmot]

The multi checkbox custom field's values appear in one column only. How can I make values appear in 3 columns layout horizontally?

[Nic Brough -Adaptavist-]

You need to write a new field plugin to provide a different layout (you might be able to botch something with javascript or maybe even css, but the correct answer is to have a dedicated field type for it)