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	東京は、日本の関東平野中央部の東京湾に面する地域、もしくは同域に存在する世界都市である。都市圏として世界最大の<dfn title="世界の都市圏人口の順位を参照">人口・経済力を擁しており</dfn>、現在の日本の<dfn title="「首都」に関しては、様々な辞典類・事典類にそう記述されているが、直接的に首都が東京であることを定めた法令は存在しない">事実上の首都である</dfn>。

江戸幕府の所在地・江戸が慶応4年7月(1868年9月)に「東京」に名称変更された。都が京都から明治2年3月28日に<dfn title="広辞苑第六版「東京」より">「東京」に遷されている。</dfn>


                dfn[title] {
	cursor: help;
	position: relative;
	font-style: normal;
dfn[title]:after {
	content: "*";
	color: red;
	display: inline;
	text-align: right;
	white-space: nowrap;
	vertical-align: super;
	font-weight: bold;
	font-size: 0.6em;
	padding-left: 2px;
dfn[title]:hover:after {
	content: " (" attr(title) ")";
	min-width: 100%;
	color: red;
	vertical-align: inherit;
	font-size: inherit;
	padding-left: 0;

hgroup {
	width: 500px;
	margin: 20px auto;

h1 {
	font-weight: 700;
	font-size: 30px;
	margin-bottom: 0px;