Help me understand this piece of code

[FernandoBasso]

Given this piece of code, I don't understand the part I commented:

function attr(elem, name, value) { // {{{

    if (!name || name.constructor != String) return '';

    /* I don't understand the [name] = name, and the relation
     * of [name] with the previous code in the line. */
    name = {'for': 'htmlFor', 'class': 'className'}[name] = name; // I don't understand this line.

    if (typeof value != 'undefined') {

        elem[name] = value;

        if (elem.setAttribute)
            elem.setAttribute(attrName, attrValue);
    }

    return elem[name] || elem.getAttribute(name) || '';
} // }}}

I'll greatelly appreciate any clarification on that. A link with some doc related
to that is equally interesting. Thanks in a advance.