DOMOutputSpec

A description of a DOM structure. Can be either a string, which is interpreted as a text node, a DOM node, which is interpreted as itself, a {dom, contentDOM} object, or an array.

An array describes a DOM element. The first value in the array should be a string—the name of the DOM element, optionally prefixed by a namespace URL and a space. If the second element is plain object, it is interpreted as a set of attributes for the element. Any elements after that (including the 2nd if it's not an attribute object) are interpreted as children of the DOM elements, and must either be valid DOMOutputSpec values, or the number zero.

The number zero (pronounced “hole”) is used to indicate the place where a node's child nodes should be inserted. If it occurs in an output spec, it should be the only child element in its parent node.