(doc) Problem: Background of conditional templating is not documented.

[hastebrot]

Proposed solution: First document the cornerstones:

polymer/lib/mixins/element-mixin.html will stamp the template when super.ready() is called in the custom element. It calls _stampTemplate() from Polymer.TemplateStamp.

ready() {
  if (this._template) {
    this.root = this._stampTemplate(this._template);
    this.$ = this.root.$;
  }
  super.ready();
}

polymer/lib/elements/dom-repeat.html.

<p>Employee list:</p>
<template is="dom-repeat" items="{{employees}}" as="item">
  <employee-item first="{{item.first}}" last="{{item.last}}"></employee-item>
</template>

[hastebrot]

For Polymer 2.x, you do not need to provide your own Promise polyfill if you are using the web components polyfills. Because the web components v1 APIs depend on Promise, a promise polyfill is loaded when needed by the v1 polyfills (web-components-lite.js or webcomponents-loader.js).

— https://github.com/PolymerElements/iron-ajax/blob/master/README.md