lib/Ext/core/Ext-more.js
function(el, prefix) {
        if (el && el.id) {
            return el.id;
        }

        el = Ext.getDom(el) || {};

        if (el === document || el === document.documentElement) {
            el.id = 'ext-app';
        }
        else if (el === document.body) {
            el.id = 'ext-body';
        }
        else if (el === window) {
            el.id = 'ext-window';
        }

        el.id = el.id || ((prefix || 'ext-') + (++Ext.idSeed));

        return el.id;
    }
function(el, prefix) {
        if (el && el.id) {
            return el.id;
        }

        el = Ext.getDom(el) || {};

        if (el === document || el === document.documentElement) {
            el.id = 'ext-app';
        }
        else if (el === document.body) {
            el.id = 'ext-body';
        }
        else if (el === window) {
            el.id = 'ext-window';
        }

        el.id = el.id || ((prefix || 'ext-') + (++Ext.idSeed));

        return el.id;
    }
Generates unique ids. If the element is passes and it already has an `id`, it is unchanged.
@param {Mixed} el (optional) The element to generate an id for.
@param {String} [prefix=ext-gen] (optional) The `id` prefix.
@return {String} The generated `id`.