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third_party/polymer/v1_0/components-chromium/iron-list/README.md

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-[![Build status](https://travis-ci.org/PolymerElements/iron-list.svg?branch=master)](https://travis-ci.org/PolymerElements/iron-list)
-
-_[Demo and API docs](https://elements.polymer-project.org/elements/iron-list)_
-
-
-##&lt;iron-list&gt;
-
-`iron-list` displays a virtual, 'infinite' list. The template inside
-the iron-list element represents the DOM to create for each list item.
-The `items` property specifies an array of list item data.
-
-For performance reasons, not every item in the list is rendered at once;
-instead a small subset of actual template elements *(enough to fill the viewport)*
-are rendered and reused as the user scrolls. As such, it is important that all
-state of the list template be bound to the model driving it, since the view may
-be reused with a new model at any time. Particularly, any state that may change
-as the result of a user interaction with the list item must be bound to the model
-to avoid view state inconsistency.
-
-__Important:__ `iron-list` must either be explicitly sized, or delegate scrolling to an
-explicitly sized parent. By "explicitly sized", we mean it either has an explicit
-CSS `height` property set via a class or inline style, or else is sized by other
-layout means (e.g. the `flex` or `fit` classes).
-
-### Template model
-
-List item templates should bind to template models of the following structure:
-
-```js
-{
-  index: 0,        // index in the item array
-  selected: false, // true if the current item is selected
-  tabIndex: -1,    // a dynamically generated tabIndex for focus management
-  item: {}         // user data corresponding to items[index]
-}
-```
-
-Alternatively, you can change the property name used as data index by changing the
-`indexAs` property. The `as` property defines the name of the variable to add to the binding
-scope for the array.
-
-For example, given the following `data` array:
-
-##### data.json
-
-```js
-[
-  {"name": "Bob"},
-  {"name": "Tim"},
-  {"name": "Mike"}
-]
-```
-
-The following code would render the list (note the name and checked properties are
-bound from the model object provided to the template scope):
-
-```html
-<template is="dom-bind">
-  <iron-ajax url="data.json" last-response="{{data}}" auto></iron-ajax>
-  <iron-list items="[[data]]" as="item">
-    <template>
-      <div>
-        Name: [[item.name]]
-      </div>
-    </template>
-  </iron-list>
-</template>
-```
-
-### Accessibility
-
-`iron-list` automatically manages the focus state for the items. It also provides
-a `tabIndex` property within the template scope that can be used for keyboard navigation.
-For example, users can press the up and down keys to move to previous and next
-items in the list:
-
-```html
-<iron-list items="[[data]]" as="item">
-  <template>
-    <div tabindex$="[[tabIndex]]">
-      Name: [[item.name]]
-    </div>
-  </template>
-</iron-list>
-```
-
-### Styling
-
-You can use the `--iron-list-items-container` mixin to style the container of items:
-
-```css
-iron-list {
- --iron-list-items-container: {
-    margin: auto;
-  };
-}
-```
-
-### Resizing
-
-`iron-list` lays out the items when it receives a notification via the `iron-resize` event.
-This event is fired by any element that implements `IronResizableBehavior`.
-
-By default, elements such as `iron-pages`, `paper-tabs` or `paper-dialog` will trigger
-this event automatically. If you hide the list manually (e.g. you use `display: none`)
-you might want to implement `IronResizableBehavior` or fire this event manually right
-after the list became visible again. For example:
-
-```js
-document.querySelector('iron-list').fire('iron-resize');
-```
-
-### When should `<iron-list>` be used?
-
-`iron-list` should be used when a page has significantly more DOM nodes than the ones
-visible on the screen. e.g. the page has 500 nodes, but only 20 are visible at the time.
-This is why we refer to it as a `virtual` list. In this case, a `dom-repeat` will still
-create 500 nodes which could slow down the web app, but `iron-list` will only create 20.
-
-However, having an `iron-list` does not mean that you can load all the data at once.
-Say, you have a million records in the database, you want to split the data into pages
-so you can bring a page at the time. The page could contain 500 items, and iron-list
-will only render 20.
-
-