○ Item elements : 브라우저에 콘텐츠가 없어도 보이는 태그 또는 콘텐츠를 꾸며주는 태그
<e.g.> a, video, button, audio, input, map, label, canvas, img, talbe 등
<e.g code>
<p>
This span is an <span class="highlight">inline-level element</span>; its
background has been colored to display both the beginning and end of the
element's influence. Input elements, like <input type="radio" /> and
<input type="checkbox" />, are also inline-level content.
</p>
○ Box elements : 브라우저에 콘텐츠가 없지만 태그 또는 영역 or 의미를 정의하는 태그
<e.g code>
<div>
<p>
This the first paragraph. The background color of these paragraphs have been
colored to distinguish them from their parent element.
</p>
<p>This is the second paragraph.</p>
</div>
