2018-10-10 18:03:03 -04:00
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---
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id: 587d778d367417b2b2512aaa
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2020-12-16 00:37:30 -07:00
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title: 使用自定义 CSS 让元素仅对屏幕阅读器可见
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2018-10-10 18:03:03 -04:00
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challengeType: 0
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2020-02-11 17:06:41 +08:00
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videoUrl: 'https://scrimba.com/c/cJ8QGkhJ'
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forumTopicId: 301020
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2021-01-13 03:31:00 +01:00
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dashedName: make-elements-only-visible-to-a-screen-reader-by-using-custom-css
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2018-10-10 18:03:03 -04:00
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---
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2020-12-16 00:37:30 -07:00
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# --description--
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2021-03-12 07:30:30 -07:00
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到目前为止，所有关于可访问性的挑战都没有使用 CSS。 这是为了在介绍视觉设计方面之前强调使用逻辑结构和有语义意义的标签的重要性。
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2020-12-16 00:37:30 -07:00
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2021-02-06 04:42:36 +00:00
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但如果我们想在页面中添加一些只对屏幕阅读器可见的内容，可以用 CSS 来实现。 当信息为视觉格式（例如图表）时，但屏幕阅读器用户需要备用文稿（例如表格）来访问数据，在这种情况下， 使用 CSS 将屏幕的只读元素放到浏览器窗口可视区域之外。
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2020-12-16 00:37:30 -07:00
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2020-02-11 17:06:41 +08:00
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举个例子：
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```css
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.sr-only {
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position: absolute;
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left: -10000px;
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width: 1px;
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height: 1px;
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top: auto;
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overflow: hidden;
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}
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```
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2021-01-08 11:20:48 -08:00
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**注意：**以下的 CSS 解决方案与上面的结果不同：
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2020-12-16 00:37:30 -07:00
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2020-02-11 17:06:41 +08:00
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<ul>
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2021-01-08 11:20:48 -08:00
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<li><code>display: none;</code> 或 <code>visibility: hidden;</code> 会把内容彻底隐藏起来，屏幕阅读器也无法获取这些内容。</li>
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<li>如果把值设置为 0px，如 <code>width: 0px; height: 0px;</code>，意味着让元素脱离文档流，这样做同样也会让屏幕阅读器忽略此元素。</li>
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2020-02-11 17:06:41 +08:00
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</ul>
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2018-10-10 18:03:03 -04:00
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2020-12-16 00:37:30 -07:00
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# --instructions--
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2018-10-10 18:03:03 -04:00
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2021-02-06 04:42:36 +00:00
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Camper Cat 为他的训练页面创建了一个十分酷炫的条形图。 考虑到可访问性，他还将数据放入到了一个表格中，供屏幕阅读器用户使用。 表格已有一个 `sr-only` class，但是还没有添加 CSS 规则。 设置 `position` 的值为 `absolute`，`left` 的值为 `-10000px`，`width` 和 `height` 的值均为 `1px`。
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2020-12-16 00:37:30 -07:00
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# --hints--
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2021-02-06 04:42:36 +00:00
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设置 `sr-only` class 的 `position` 属性值为 `absolute`。
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2020-12-16 00:37:30 -07:00
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```js
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assert($('.sr-only').css('position') == 'absolute');
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2018-10-10 18:03:03 -04:00
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```
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2021-02-06 04:42:36 +00:00
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设置 `sr-only` class 的 `left` 属性值为`-10000px`。
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2018-10-10 18:03:03 -04:00
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2020-12-16 00:37:30 -07:00
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```js
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assert($('.sr-only').css('left') == '-10000px');
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```
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2018-10-10 18:03:03 -04:00
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2021-02-16 15:21:30 -07:00
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设置 `sr-only` class 的 `width` 属性值为 `1` 像素。
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2018-10-10 18:03:03 -04:00
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2020-12-16 00:37:30 -07:00
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```js
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assert(code.match(/width:\s*?1px/gi));
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```
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2018-10-10 18:03:03 -04:00
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2021-02-16 15:21:30 -07:00
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设置 `sr-only` class 的 `height` 属性值为 `1` 像素。
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2018-10-10 18:03:03 -04:00
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2020-12-16 00:37:30 -07:00
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```js
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assert(code.match(/height:\s*?1px/gi));
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2018-10-10 18:03:03 -04:00
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```
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2020-02-11 17:06:41 +08:00
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2021-01-13 03:31:00 +01:00
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# --seed--
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## --seed-contents--
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```html
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<head>
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<style>
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.sr-only {
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position: ;
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left: ;
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width: ;
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height: ;
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top: auto;
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overflow: hidden;
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}
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</style>
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</head>
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<body>
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<header>
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<h1>Training</h1>
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<nav>
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<ul>
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<li><a href="#stealth">Stealth & Agility</a></li>
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<li><a href="#combat">Combat</a></li>
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<li><a href="#weapons">Weapons</a></li>
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</ul>
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</nav>
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</header>
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<section>
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<h2>Master Camper Cat's Beginner Three Week Training Program</h2>
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<figure>
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<!-- Stacked bar chart of weekly training -->
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<p>[Stacked bar chart]</p>
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<br />
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<figcaption>Breakdown per week of time to spend training in stealth, combat, and weapons.</figcaption>
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</figure>
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<table class="sr-only">
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<caption>Hours of Weekly Training in Stealth, Combat, and Weapons</caption>
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<thead>
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<tr>
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<th></th>
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<th scope="col">Stealth & Agility</th>
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<th scope="col">Combat</th>
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<th scope="col">Weapons</th>
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<th scope="col">Total</th>
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</tr>
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</thead>
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<tbody>
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<tr>
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<th scope="row">Week One</th>
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<td>3</td>
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<td>5</td>
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<td>2</td>
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<td>10</td>
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</tr>
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<tr>
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<th scope="row">Week Two</th>
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<td>4</td>
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<td>5</td>
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<td>3</td>
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<td>12</td>
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</tr>
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<tr>
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<th scope="row">Week Three</th>
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<td>4</td>
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<td>6</td>
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<td>3</td>
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<td>13</td>
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</tr>
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</tbody>
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</table>
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</section>
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<section id="stealth">
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<h2>Stealth & Agility Training</h2>
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<article><h3>Climb foliage quickly using a minimum spanning tree approach</h3></article>
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<article><h3>No training is NP-complete without parkour</h3></article>
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</section>
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<section id="combat">
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<h2>Combat Training</h2>
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<article><h3>Dispatch multiple enemies with multithreaded tactics</h3></article>
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<article><h3>Goodbye, world: 5 proven ways to knock out an opponent</h3></article>
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</section>
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<section id="weapons">
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<h2>Weapons Training</h2>
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<article><h3>Swords: the best tool to literally divide and conquer</h3></article>
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<article><h3>Breadth-first or depth-first in multi-weapon training?</h3></article>
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</section>
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<footer>© 2018 Camper Cat</footer>
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</body>
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```
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2020-12-16 00:37:30 -07:00
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# --solutions--
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2021-01-13 03:31:00 +01:00
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```html
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<head>
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<style>
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.sr-only {
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position: absolute;
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left: -10000px;
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width: 1px;
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height: 1px;
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top: auto;
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overflow: hidden;
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}
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</style>
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</head>
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<body>
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<header>
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<h1>Training</h1>
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<nav>
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<ul>
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<li><a href="#stealth">Stealth & Agility</a></li>
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<li><a href="#combat">Combat</a></li>
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<li><a href="#weapons">Weapons</a></li>
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</ul>
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</nav>
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</header>
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<section>
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<h2>Master Camper Cat's Beginner Three Week Training Program</h2>
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<figure>
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<!-- Stacked bar chart of weekly training -->
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<p>[Stacked bar chart]</p>
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<br />
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<figcaption>Breakdown per week of time to spend training in stealth, combat, and weapons.</figcaption>
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</figure>
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<table class="sr-only">
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<caption>Hours of Weekly Training in Stealth, Combat, and Weapons</caption>
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<thead>
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<tr>
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<th></th>
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<th scope="col">Stealth & Agility</th>
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<th scope="col">Combat</th>
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<th scope="col">Weapons</th>
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<th scope="col">Total</th>
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</tr>
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</thead>
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<tbody>
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<tr>
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<th scope="row">Week One</th>
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<td>3</td>
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<td>5</td>
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<td>2</td>
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<td>10</td>
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</tr>
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<tr>
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<th scope="row">Week Two</th>
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<td>4</td>
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<td>5</td>
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<td>3</td>
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<td>12</td>
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</tr>
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<tr>
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<th scope="row">Week Three</th>
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<td>4</td>
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<td>6</td>
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<td>3</td>
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<td>13</td>
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</tr>
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</tbody>
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</table>
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</section>
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<section id="stealth">
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<h2>Stealth & Agility Training</h2>
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<article><h3>Climb foliage quickly using a minimum spanning tree approach</h3></article>
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<article><h3>No training is NP-complete without parkour</h3></article>
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</section>
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<section id="combat">
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<h2>Combat Training</h2>
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<article><h3>Dispatch multiple enemies with multithreaded tactics</h3></article>
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<article><h3>Goodbye, world: 5 proven ways to knock out an opponent</h3></article>
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</section>
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<section id="weapons">
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<h2>Weapons Training</h2>
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<article><h3>Swords: the best tool to literally divide and conquer</h3></article>
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<article><h3>Breadth-first or depth-first in multi-weapon training?</h3></article>
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</section>
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<footer>© 2018 Camper Cat</footer>
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</body>
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```
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