HTML 仕様書で定義されている標準メタデータ名
HTML 仕様書は、以下の一連の標準メタデータ名を定義しています。
-
application-name
: ウェブページで動作しているアプリケーションの名前です。注:- ブラウザーはアプリケーションを識別するためにこれを使用することがあります。これはふつうアプリケーション名が含まれるものの、文書名や状態などの情報も含まれる
<title>
要素とは異なります。 - 単なるウェブサイトにはアプリケーション名を定義するべきではありません。
- ブラウザーはアプリケーションを識別するためにこれを使用することがあります。これはふつうアプリケーション名が含まれるものの、文書名や状態などの情報も含まれる
author
: この文書の著者です。description
: ページの内容を短く正確に要約したものです。 Firefox や Opera など一部のブラウザーは、これをブックマークされたページの既定の説明として使用します。generator
: このページを生成したソフトウェアの識別子です。keywords
: ページのコンテンツに関連する語句で、カンマ区切りです。referrer
: この文書からリクエストを送信するための HTTP のReferer
ヘッダーの内容です。<meta name="referrer">
のcontent
属性の値no-referrer
HTTP の Referer
ヘッダーを送信しません。origin
文書のオリジンを送信します。 no-referrer-when-downgrade
現在のページと同等の安全性の URL (HTTP(S)→HTTPS) にはリファラーとして URL 全体を送信しますが、安全性が低い URL (HTTPS→HTTP) には送信しません。これは既定の動作です。 origin-when-cross-origin
同一オリジンへのリクエストでは URL 全体 (引数を除く) を送信しますが、他の場合はオリジンのみ送信します。 same-origin
同一オリジンにはリファラーを送信しますが、オリジン間リクエストにはリファラーを含めません。 strict-origin
安全性が同等とみられる宛先 (HTTP(S)→HTTPS) に対しては、リファラーとして文書のオリジンのみを送信しますが、安全性が劣る宛先 (HTTPS→HTTP) には送信しません。 strict-origin-when-cross-origin
同一オリジンへのリクエストでは、 URL 全体 (引数を除く) を送信します。現在のページと安全性が同等であると見られる宛先 (HTTP(S)→HTTPS) にはオリジンを送信します。それ以外は、リファラーを送信しません。 unsafe-URL
同一オリジンまたはオリジン間リクエストで、 URL 全体 (引数を除く) を送信します。 注:- Dynamically inserting
<meta name="referrer">
(withdocument.write()
orappendChild()
) makes the referrer behaviour unpredictable. - When several conflicting policies are defined, the
no-referrer
policy is applied.
- Dynamically inserting
theme-color
: indicates a suggested color that user agents should use to customize the display of the page or of the surrounding user interface. Thecontent
attribute contains a valid CSS<color>
.
他の仕様書で定義されている標準メタデータ名
The CSS Color Adjustment specification defines the following metadata name:
-
color-scheme
: specifies one or more color schemes with which the document is compatible.The browser will use this information in tandem with the user's browser or device settings to determine what colors to use for everything from background and foregrounds to form controls and scrollbars. The primary use for
<meta name="color-scheme">
is to indicate compatibility with—and order of preference for—light and dark color modes.The value of the
content
property forcolor-scheme
may be one of the following:normal
- The document is unaware of color schemes and should simply be rendered using the default color palette.
- [
light
|dark
]+ - One or more color schemes supported by the document. Specifying the same color scheme more than once has the same effect as specifying it only once. Indicating multiple color schemes indicates that the first scheme is preferred by the document, but that the second specified scheme is acceptable if the user prefers it.
only light
- Indicates that the document only supports light mode, with a light background and dark foreground colors. By specification,
only dark
is not valid, because forcing a document to render in dark mode when it isn't truly compatible with it can result in unreadable content; all major browsers default to light mode if not otherwise configured.
For example, to indicate that a document prefers dark mode but does render functionally in light mode as well:
<meta name="color-scheme" content="dark light">
This works at the document level in the same way that the CSS
color-scheme
property lets individual elements specify their preferred and accepted color schemes. Your styles can adapt to the current color scheme using theprefers-color-scheme
CSS media feature.
The CSS Device Adaptation specification defines the following metadata name:
-
viewport
: gives hints about the size of the initial size of the viewport. Used by mobile devices only.Values for the content of <meta name="viewport">
値 Possible subvalues 解説 width
A positive integer number, or the text device-width
Defines the pixel width of the viewport that you want the web site to be rendered at. height
A positive integer, or the text device-height
Defines the height of the viewport. Not used by any browser. initial-scale
A positive number between 0.0
and10.0
Defines the ratio between the device width ( device-width
in portrait mode ordevice-height
in landscape mode) and the viewport size.maximum-scale
A positive number between 0.0
and10.0
Defines the maximum amount to zoom in. It must be greater or equal to the minimum-scale
or the behaviour is undefined. Browser settings can ignore this rule and iOS10+ ignores it by default.minimum-scale
A positive number between 0.0
and10.0
Defines the minimum zoom level. It must be smaller or equal to the maximum-scale
or the behaviour is undefined. Browser settings can ignore this rule and iOS10+ ignores it by default.user-scalable
yes
orno
If set to no
, the user is not able to zoom in the webpage. The default isyes
. Browser settings can ignore this rule, and iOS10+ ignores it by default.viewport-fit
auto
,contain
orcover
The
auto
value doesn’t affect the initial layout viewport, and the whole web page is viewable.The
contain
value means that the viewport is scaled to fit the largest rectangle inscribed within the display.The
cover
value means that the viewport is scaled to fill the device display. It is highly recommended to make use of the safe area inset variables to ensure that important content doesn't end up outside the display.Notes:- Though unstandardized, this declaration is respected by most mobile browsers due to de-facto dominance.
- The default values may vary between devices and browsers.
- To learn about this declaration in Firefox for Mobile, see this article.
ビューポートの拡大縮小についてのアクセシビリティの考慮
Disabling zooming capabilities by settinguser-scalable
to a value ofno
prevents people experiencing low vision conditions from being able to read and understand page content.- MDN Understanding WCAG, Guideline 1.4 explanations
- Understanding Success Criterion 1.4.4 | W3C Understanding WCAG 2.0
関連情報
The
@viewport
CSS at-rule.
その他のメタデータ名
The WHATWG Wiki MetaExtensions page contains a large set of non-standard metadata names that have not been formally accepted yet; however, some of the names included there are already used quite commonly in practice — including the following:
creator
: the name of the creator of the document, such as an organization or institution. If there are more than one, several<meta>
elements should be used.googlebot
, a synonym ofrobots
, is only followed by Googlebot (the indexing crawler for Google).publisher
: the name of the document's publisher.robots
: the behaviour that cooperative crawlers, or "robots", should use with the page. It is a comma-separated list of the values below:Values for the content of <meta name="robots">
値 解説 Used by index
Allows the robot to index the page (default). All noindex
Requests the robot to not index the page. All follow
Allows the robot to follow the links on the page (default). All nofollow
Requests the robot to not follow the links on the page. All all
Equivalent to index, follow
Google none
Equivalent to noindex, nofollow
Google noarchive
Requests the search engine not to cache the page content. Google, Yahoo, Bing nosnippet
Prevents displaying any description of the page in search engine results. Google, Bing noimageindex
Requests this page not to appear as the referring page of an indexed image. Google nocache
Synonym of noarchive
.Bing Notes:- Only cooperative robots follow these rules. Do not expect to prevent e-mail harvesters with them.
- The robot still needs to access the page in order to read these rules. To prevent bandwidth consumption, use a robots.txt file.
- If you want to remove a page,
noindex
will work, but only after the robot visits the page again. Ensure that therobots.txt
file is not preventing revisits. - Some values are mutually exclusive, like
index
andnoindex
, orfollow
andnofollow
. In these cases the robot's behaviour is undefined and may vary between them. - Some crawler robots, like Google, Yahoo and Bing, support the same values for the HTTP header
X-Robots-Tag
; this allows non-HTML documents like images to use these rules.
仕様書
ブラウザーの互換性
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