What Tag in HTML Should I Use Without Special Meaning, Only to Carry Meta Data

What tag in HTML should I use without special meaning, only to carry meta data?

The data applies to the div, the attributes should be on the div. If you want to format your code with one item per line, then you can.

<div class="item"
     data-id="123"
     data-type="sometype"
     data-validate="true">

There are no elements designed for storing meta data that go in the document body.

Using an individual tag without breaking the standards?

Having to support HTML 4.01 and HTML5 makes this hard. You can’t use meta-name elements (would work for HTML 4.01, but they have to be registered for HTML5), you can’t use custom data-* attributes (not allowed in HTML 4.01), you can’t use Microdata (only defined for HTML5+), you can’t use custom elements (only defined for HTML5+).

I can think of two ways.

`script` element as data block

In HTML5, the script element can also be used for data blocks. Examples: text/html, text/plain.

The HTML 4.01 spec doesn’t define it like that, but it should still be possible/valid (it’ll understand it as "script", but user agents are not expected to try to run it if they don’t recognize the content type as possible for scripts).

Drawback: The content is not part of the document’s DOM.

RDFa

It’s allowed in HTML 4.01 and HTML5 (you might have to adapt the DOCTYPE for the older HTML versions, e.g., for XHTML).

You can’t use custom elements, but you can add property and content attributes (for name-value pairs), and you could use typeof for "items" (e.g., what you would use the element name for), and you can make use of meta and link elements (visually hidden by default) in the body.

<div vocab="https://api.example.com/voc#" class="the-hidden-information">

  <div typeof="Item-123">
    <meta property="foo1" content="bar1" />
    <meta property="foo2" content="bar2" />
  </div>

  <div typeof="Item-345">
    <meta property="foo1" content="bar1" />
    <link property="foo5" href="/some-url" />
  </div>

</div>

(when using RDFa 1.0 instead of 1.1, you’d have to use xmlns instead of vocab)

Best practice for meta data in a html document?

W3C validation is meaningless. HTML != XML, so there isn't any schema to validate it. No browser will choke because you added a meta element with an unregistered name. If you really are worried, you could use the data attribute on a meta element like:

<meta data-details="52:AS6[rxSdsMd4RgYXJgeabsRAVBZ:0406139009]" data-policyId="0123456789" />

at least then you know no future spec will give meaning to your data.

For more info read: http://www.whatwg.org/specs/web-apps/current-work/multipage/elements.html#custom-data-attribute

Meta Tag in Body

The <meta>-tag is part of the 4.2 Document metadata. Therefor it can only appear in the <head>-section of a document. Your solution using a <span> or a <div> or even a list for multiple errors is just fine for your purpose.

When should script tags be visible and why can they?

The HTML5 specification defines a style sheet that user agents (like browsers) are expected to use. Section 10.3.1 lists the styles for "Hidden elements":

@namespace url(http://www.w3.org/1999/xhtml);

[hidden], area, base, basefont, datalist, head, link,
meta, noembed, noframes, param, rp, script, source, style, template, track, title {
  display: none;
}

embed[hidden] { display: inline; height: 0; width: 0; }

As you can see, it applies display: none; to script.

This is the only "barrier" between your users and hidden script elements. It’s perfectly fine and intended to be able to overwrite styles from user-agent style sheets within author style sheets (and of course also within user style sheets).

Why someone might want to use it? One use case is displaying content without having to escape characters like </>, similar to the old xmp element. The script element can be used not only for scripts, but also for data blocks (i.e., for anything with a MIME type).

Microdata vs. the data attribute in modular HTML5

Both ways are possible.

Microdata is not only for "typed data". You could define your own Microdata vocabulary, if you like. But you could also use a "local" one (emphasis mine):

The examples in the previous section show how information could be marked up on a page that doesn't expect its microdata to be re-used. Microdata is most useful, though, when it is used in contexts where other authors and readers are able to cooperate to make new uses of the markup.

However, if you want to use some other Microdata vocabulary (e.g. schema.org) on your pages in the future, you might get some conflicts with your "local" Microdata. So I’d not use Microdata if it doesn’t offer you benefits over data-* attributes.

Regarding the meta element: You can get something similar with data-* attributes, too. In HTML5, the script element can be used for "data blocks". So you could use something like:

<div class="wrapper" id="module1">
  <script type="text/plain" data-userDoesSomething="alert('Data attributes are better!');">
  </script>
  Module-specific content
</div>

<div class="wrapper" id="module1">
  <script type="text/plain" data-userDoesSomething>
    alert('Data attributes are better!');
  </script>
  Module-specific content
</div>

<!-- etc. -->

Instead of text/plain, you could use whatever suits your needs (JSON, HTML, …).

What does meta http-equiv=X-UA-Compatible content=IE=edge do?

November 2021 Update

As this answer is now 10+ years old my recommendation would be to leave this tag out altogether, unless you must support old legacy browsers.

October 2015 Update

This answer was posted several years ago and now the question really should be should you even consider using the X-UA-Compatible tag on your site? with the changes Microsoft has made to its browsers (more on those below).

Depending upon what Microsoft browsers you support you may not need to continue using the X-UA-Compatible tag. If you need to support IE9 or IE8, then I would recommend using the tag. If you only support the latest browsers (IE11 and/or Edge) then I would consider dropping this tag altogether. If you use Twitter Bootstrap and need to eliminate validation warnings, this tag must appear in its specified order. Additional info below:

The X-UA-Compatible meta tag allows web authors to choose what version of Internet Explorer the page should be rendered as. IE11 has made changes to these modes; see the IE11 note below. Microsoft Edge, the browser that replaced IE11, only honors the X-UA-Compatible meta tag in certain circumstances. See the Microsoft Edge note below.

According to Microsoft, when using the X-UA-Compatible tag, it should be as high as possible in your document head:

If you are using the X-UA-Compatible META tag you want to place it as close to the top of the page's HEAD as possible. Internet Explorer begins interpreting markup using the latest version. When Internet Explorer encounters the X-UA-Compatible META tag it starts over using the designated version's engine. This is a performance hit because the browser must stop and restart analyzing the content.

Here are your options:

"IE=edge"
"IE=11"
"IE=EmulateIE11"
"IE=10"
"IE=EmulateIE10"
"IE=9"
"IE=EmulateIE9
"IE=8"
"IE=EmulateIE8"
"IE=7"
"IE=EmulateIE7"
"IE=5"

To attempt to understand what each means, here are definitions provided by Microsoft:

Internet Explorer supports a number of document compatibility modes that enable different features and can affect the way content is displayed:

Edge mode tells Internet Explorer to display content in the highest mode available. With Internet Explorer 9, this is equivalent to IE9 mode. If a future release of Internet Explorer supported a higher compatibility mode, pages set to edge mode would appear in the highest mode supported by that version. Those same pages would still appear in IE9 mode when viewed with Internet Explorer 9.
Internet Explorer supports a number of document compatibility modes that enable different features and can affect the way content is displayed:

IE11 mode provides the highest support available for established and emerging industry standards, including the HTML5, CSS3 and others.

IE10 mode provides the highest support available for established and emerging industry standards, including the HTML5, CSS3 and others.

IE9 mode provides the highest support available for established and emerging industry standards, including the HTML5 (Working Draft), W3C Cascading Style Sheets Level 3 Specification (Working Draft), Scalable Vector Graphics (SVG) 1.0 Specification, and others. [Editor Note: IE 9 does not support CSS3 animations].

IE8 mode supports many established standards, including the W3C Cascading Style Sheets Level 2.1 Specification and the W3C Selectors API; it also provides limited support for the W3C Cascading Style Sheets Level 3 Specification (Working Draft) and other emerging standards.

IE7 mode renders content as if it were displayed in standards mode by Internet Explorer 7, whether or not the page contains a <!DOCTYPE> directive.

Emulate IE9 mode tells Internet Explorer to use the <!DOCTYPE> directive to determine how to render content. Standards mode directives are displayed in IE9 mode and quirks mode directives are displayed in IE5 mode. Unlike IE9 mode, Emulate IE9 mode respects the <!DOCTYPE> directive.

Emulate IE8 mode tells Internet Explorer to use the <!DOCTYPE> directive to determine how to render content. Standards mode directives are displayed in IE8 mode and quirks mode directives are displayed in IE5 mode. Unlike IE8 mode, Emulate IE8 mode respects the <!DOCTYPE> directive.

Emulate IE7 mode tells Internet Explorer to use the <!DOCTYPE> directive to determine how to render content. Standards mode directives are displayed in Internet Explorer 7 standards mode and quirks mode directives are displayed in IE5 mode. Unlike IE7 mode, Emulate IE7 mode respects the <!DOCTYPE> directive. For many web sites, this is the preferred compatibility mode.

IE5 mode renders content as if it were displayed in quirks mode by Internet Explorer 7, which is very similar to the way content was displayed in Microsoft Internet Explorer 5.

IE10 NOTE: As of IE10, quirks mode behaves differently than it did in earlier versions of the browser. In IE9 and earlier versions, quirks mode restricted the webpage to the features supported by IE5.5. In IE10, quirks mode conforms to the differences specified in the HTML5 specification.

Personally, I always choose the http-equiv="X-UA-Compatible" content="IE=edge" meta tag, as older versions have plenty of bugs, and I do not want IE to decide to go into "Compatibility mode" and show my site as IE7 vs IE8 or 9. I always prefer the latest version of IE.

IE11

From Microsoft:

Starting with IE11, edge mode is the preferred document mode; it represents the highest support for modern standards available to the browser.

Use the HTML5 document type declaration to enable edge mode:

<!doctype html>

Edge mode was introduced in Internet Explorer 8 and has been available in each subsequent release. Note that the features supported by edge mode are limited to those supported by the specific version of the browser rendering the content.

Starting with IE11, document modes are deprecated and should no longer be used, except on a temporary basis. Make sure to update sites that rely on legacy features and document modes to reflect modern standards.

If you must target a specific document mode so that your site functions while you rework it to support modern standards and features, be aware that you're using a transitional feature, one that may not be available in future versions.

If you currently use the x-ua-compatible header to target a legacy document mode, it's possible your site won't reflect the best experience available with IE11.

Microsoft Edge (Replacement for Internet Explorer that comes bundled with Windows 10)

Information on X-UA-Compatible meta tag for the "Edge" version of IE. From Microsoft:

Introducing the “living” Edge document mode

As we announced in August 2013, we are deprecating document modes as of IE11. With our latest platform updates, the need for legacy document modes is primarily limited to Enterprise legacy web apps. With new architectural changes, these legacy document modes will be isolated from changes in the “living” Edge mode, which will help to guarantee a much higher level of compatibility for customers who depend on those modes and help us move even faster on improvements in Edge. IE will still honor document modes served by intranet sites, sites on the Compatibility View list, and when used with Enterprise Mode only.

Public Internet sites will be rendered with the new Edge mode platform (ignoring X-UA-Compatible). It is our goal that Edge is the "living" document mode from here out and no further document modes will be introduced going forward.

With the changes in Microsoft Edge to no longer support document modes in most cases, Microsoft has a tool to scan your site to check and see if it has code that is not compatible with Edge.

Chrome=1 Info for IE

There is also chrome=1 that you can use or use together with one of the above options like: <meta http-equiv="X-UA-Compatible" content="IE=Edge,chrome=1">. chrome=1 is for Google's Chrome Frame which is defined as:

Google Chrome Frame is an open source browser plug-in. Users who have the plug-in installed have access to Google Chrome's open web technologies and speedy JavaScript engine when they open pages in the browser.

Google Chrome Frame seamlessly enhances your browsing experience in Internet Explorer. It displays Google Chrome Frame enabled sites using Google Chrome’s rendering technology, giving you access to the latest HTML5 features as well as Google Chrome’s performance and security features without in any way interrupting your usual browser usage.

When Google Chrome Frame is installed, the web just gets better without you having to think about it.

But for that plug-in to work you must use chrome=1 in the X-UA-Compatible meta tag.

More info on Chrome Frame can be found here.

Note: Google Chrome Frame only works for IE6 through IE9, and was retired on February 25, 2014. More info can be found here. Thanks to @mck for the link.

Validation:

HTML5:

The page will validate using the W3 Validator only when using <meta http-equiv="X-UA-Compatible" content="IE=Edge">. For other values it will throw the error: A meta element with an http-equiv attribute whose value is X-UA-Compatible must have a content attribute with the value IE=edge. In other words, if you have IE=edge,chrome=1 it will not validate. I ignore this error completely as modern browsers simply ignore this line of code.

If you must have completely valid code then consider doing this on the server level by setting HTTP header. As a note, Microsoft says, If both of these instructions are sent (meta and HTTP), the developer's preference (meta element) takes precedence over the web server setting (HTTP header). See olibre's answer or bitinn's answer for more details on how to set an HTTP header.

XHTML

There isn't an issue with validation when using <meta http-equiv="X-UA-Compatible" content="IE=Edge" /> as long as the tag is properly closed (i.e. /> vs >).

Twitter Bootstrap (V3 and below)

This tag has been strongly recommended by the Bootstrap team since at least 2014, and Bootlint, the linter authored by the twbs team continues to throw a warning when the tag is omitted. The linter distinguishes between warnings and errors, and as such the severity of omitting this tag may be considered minor.

For more information on X-UA-Compatible see Microsoft's Website Defining Document Compatibility.

For more information on what IE supports see caniuse.com.

For more information on Twitter Bootstrap requirements, see the bootlint project wiki page.

How to store arbitrary data for some HTML tags

Which version of HTML are you using?

In HTML 5, it is totally valid to have custom attributes prefixed with data-, e.g.

<div data-internalid="1337"></div>

In XHTML, this is not really valid. If you are in XHTML 1.1 mode, the browser will probably complain about it, but in 1.0 mode, most browsers will just silently ignore it.

If I were you, I would follow the script based approach. You could make it automatically generated on server side so that it's not a pain in the back to maintain.

How do I get the information from a meta tag with JavaScript?

You can use this:

function getMeta(metaName) {
  const metas = document.getElementsByTagName('meta');

  for (let i = 0; i < metas.length; i++) {
    if (metas[i].getAttribute('name') === metaName) {
      return metas[i].getAttribute('content');
    }
  }

  return '';
}

console.log(getMeta('video'));

What Tag in HTML Should I Use Without Special Meaning, Only to Carry Meta Data