名值对的语义与结构

小开

Hmm. dt/dd sound best for this and it is possible to offset them visually, although I do agree it's more difficult than for a table.

As for source code readability, how about putting them into one line?

<dl>
<dt>Name</dt> <dd>Value</dd>
<dt>Name</dt> <dd>Value</dd>
</dl>

I agree it's not 100% perfect, but seeing as you can use space characters for indentation:

<dl>
<dt>Property with a looooooooooong name</dt>   <dd>Value</dd>
<dt>Property with a shrt name</dt>             <dd>Value</dd>
</dl>

it might be the nicest way.

小开

I do like Unicron's idea of putting them all on one line, but another option would be to indent the value below the definition name:

<dl>
<dt>Name</dt>
<dd>Value</dd>
<dt>Name</dt>
<dd>Value</dd>
</dl>

This way might be a little easier on the eye in ridiculously long definitions (although if you're using ridiculously wrong definitions then perhaps a definition list isn't what you really want after all).

As for the rendering on screen, a fat bottom margin applied to the dd is plenty visual separation.

小开

I think a definition list is probably a bad idea. Semantically, they are used for definitions. Other key-value lists will often differ from definition titles and descriptions.

A table is one way to go, but what about an unordered list?

<ul>
<li class="key-value-pair">
<span class="key">foo</span>
<span class="value">bar</span>
</li>
</ul>

小开

How about just placing a blank line between each pair?

This requires no special handling for long values.

<dl>
<dt>Name</dt>
<dd>Value</dd>


<dt>Name</dt>
<dd>Value</dd>


<dt>Name</dt>
<dd>Value</dd>
</dl>

小开

it is difficult to properly offset the pairs visually, both in code and rendered. If I wanted to, for instance, but a border around each pair, that would be a problem.

Others before me have dealt (quite well I think) with the problem of providing visual definition in code. Which leaves the problem of rendering and CSS. This can be done quite effectively in most cases. The biggest exception is placing a border around each set of dt/dds, which is admittedly extremely tricky - perhaps impossible to style reliably.

You could do:

dt,dd{ border:solid; }
dt{ margin:10px 0 0 0; border-width:1px 1px 0 1px; }
dd{ margin:0 0 10px 0; border-width:0 1px 1px 1px; padding:0 0 0 10px; }
dd::before{ content:'→ '; }

Which works for key-value PAIRS, but presents problems if you have multiple dds within one "set" like:

<dt>Key1</dt>
<dd>Val1.1</dd>
<dd>Val1.2</dd>
<dt>Key2</dt>
<dd>Val2.1</dd>
<dd>Val2.2</dd>

However, border-styling limitations aside, doing anything else to associate sets (backgrounds, numbering, etc.) is quite possible with CSS. There's a nice overview here: http://www.maxdesign.com.au/articles/definition/

Another point I think is worth noting, if you're looking to optimally style definition-lists to provide visual separation - CSS's automatic-numbering features (counter-increment and counter-reset) can come in quite handy: http://www.w3.org/TR/CSS2/generate.html#counters

小开

最佳答案

Thanks for this interesting question. There are few more things to consider here.

What is a pair? Two elements together. So we need a tag for this. Let's say it is pair tag.

 <pair></pair>

The pair contains the key, and the corresponding value:

 <pair><key>keyname</key><value>value</value></pair>

Then, we need to list the pairs:

<pairlist>
<pair><key>keyname</key><value>value</value></pair>
<pair><key>keyname</key><value>value</value></pair>
</pairlist>

The next thing to consider, is the display of the pairs. The usual layout is the tabular one:

key value
key value

and the optional separator, which is usually colon:

key : value
key : value

The colons can be easily added via CSS, but this certainly won't work in IE.

Case described above is the ideal one. But there is no valid HTML markup to fit in this easily.

To sum up:

dl is semantically closest, for simple cases of key and value, but is hard to apply visual styles (eg. to display the pairs inline or to add red border to just hovered pair). The case which fits most for dl is glossary. But this is not the case we discuss.

The only alternative I can see in this case is to use table, like this:

<table summary="This are the key and value pairs">
<caption>Some notes about semantics</caption>
<thead class="aural if not needed">
<tr><th scope="col">keys</th><th scope="col">values</th></tr>
</thead>
<tbody class="group1">
<tr><th scope="row">key1</th><td>value1</td></tr>
<tr><th scope="row">key2</th><td>value2</td></tr>
</tbody>
<tbody class="group2">
<tr><th scope="row">key3</th><td>value3</td></tr>
<tr><th scope="row">key4</th><td>value4</td></tr>
</tbody>
</table>

One more:

<ul>
<li><strong>key</strong> value</li>
<li><strong>key</strong> value</li>
</ul>

or:

<ul>
<li><b>key</b> value</li>
<li><b>key</b> value</li>
</ul>

or, when the keys may be linked:

<ul>
<li><a href="/key1">key1</a> value</li>
<li><a href="/key2">key1</a> value</li>
</ul>

The key and value pairs are usually stored in database, and those usually store tabular data, so the table would fit best IMHO.

What do you think?

小开

What about using lists?

Ordered:

<ol>
<li title="key" value="index">value</li>
…
</ol>

Or use <ul> for an unordered list, and skip the value="index" bit.

小开

XHTML 2 introduces the ability to group terms and definitions using the di element

<!-- Do not us this code! -->
<dl>
<di>
<dt>Name</dt>
<dd>John</dd>
</di>
<di>
<dt>Age</dt>
<dd>25</dd>
</di>
</dl>

X/HTML 5 vs XHTML 2 > Enhancement To Definitions Lists

Unfortunately though, XHTML 2 is dead and HTML5 doesn't have di element

So, you can combine ul > li with dl > dt + dd :

<ul>
<li>
<dl>
<dt>Name</dt>
<dd>John</dd>
</dl>
</li>
<li>
<dl>
<dt>Age</dt>
<dd>25</dd>
</dl>
</li>
</ul>

小开

Except for the <dl> element, you've pretty much summed up all the options of HTML: limited ones.

However you're not lost, there is one option left: using a markup language that can be translated to HTML. A very good option is Markdown.

Using a table extension that some markdown engines provide, you can have code like this:

| Table header 1 | Table header 2 |
-----------------------------------
| some key       | some value     |
| another key    | another value  |

This means that you need a build step to translate the Markdown to HTML of course.

This way you get meaningful markup (table for tabular data) and maintainable code.

小开

This is not my preferred solution, but it is a clever abuse of the semantic element:

Use a new <dl> per <dt>/<dd> pair:

<div class="terms">
<dl><dt>Name 1</dt><dd>Value 1</dd></dl>
<dl><dt>Name 2</dt><dd>Value 2</dd></dl>
</div>

An example with css floats and red border on hover:

dt:after { content:":"; }
dt, dd { float: left; }
dd { margin-left: 5px }
dl { float: left; margin-left: 20px; border: 1px dashed transparent; }
dl:hover { border-color: red; }

<div class="terms">
<dl>
<dt>Name 1</dt>
<dd>Value 1</dd>
</dl><!-- etc -->
<dl><dt>Name 2</dt><dd>Value 2</dd></dl>
<dl><dt>Name 3</dt><dd>Value 3</dd></dl>
<dl><dt>Name 4</dt><dd>Value 4</dd></dl>
<dl><dt>Name 5</dt><dd>Value 5</dd></dl>
<dl><dt>Name 6</dt><dd>Value 6</dd></dl>
</div>

小开

The line from spec:

Name-value groups may be terms and definitions, metadata topics and values, questions and answers, or any other groups of name-value data.

I assume use of elements <dl>, <dt> and <dd>.

小开

Of course, you could just use HTML Custom elements. ( spec )They're completely valid HTML5.

Unfortunately, browser support isn't that great, but if rarely do we care about such pedestrian things as browser support when we're dealing with semantics. :-)

One such way you could represent it:

After registering your brand new fancy element like so:

var XKey = document.registerElement('x-key');
document.body.appendChild(new XKey());

You write markup like so:

<ul>
<li>
<x-key>Name</x-key>
Value
</li>
</ul>

The only condition that HTML Custom elements have are that they need a dash in them. Of course, you can now be super creative... if you're building an auto parts warehouse, with lists of parts and serial numbers:

<ul>
<li>
<auto-part>
<serial-number>AQ12345</serial-number>
<short-description>lorem ipsum dolor...</short-description>
<list-price>14</list-price>
</auto-part>
</li>
</ul>

You can't get much more semantic than that!

However, there IS a chance I have gone too far into semantic-shangri-la-la (a real place) and might be tempted to scale it back to something a little more generic:

<ul>
<li class='auto-part' data-serial-number="AQ12345">
<p class='short-description'>lorem ipsum dolor...</p>
<p class='list-price'>14</p>
</li>
</ul>

Or perhaps this ( if I needed to style and show the key visually )

<ul>
<li class='auto-part'>
<x-key>AQ12345<//x-key>
<p class='short-description'>lorem ipsum dolor...</p>
<p class='list-price'>14</p>
</li>
</ul>

小开

Following the specification (and further details) provided by Alexandr Antonov: use ABC0, ABC1, ABC2, and optionally div.

A combination of dl, dt, and dd is semantically fine for key-value pairs:

<dl>
<dt>Key1</dt>
<dd>Value1</dd>
<dt>Key2</dt>
<dd>Value2</dd>
</dl>

For easier styling or parsing, divs can be used as children of dl to group the key-value pairs (and makes dt and dd be grandchildren of dl):

dl { display: table; }
dl > div { display: table-row; }
dl > div > dt, dl > div > dd { display: table-cell; border: 1px solid black; padding: 0.25em; }
dl > div > dt { font-weight: bold; }

<dl>
<div>
<dt>Key1</dt>
<dd>Value1</dd>
</div>
<div>
<dt>Key2</dt>
<dd>Value2</dd>
</div>
</dl>

小开

dl {
display: grid;
grid-template-columns: auto auto;
}


dd {
margin: 0
}

<dl>
<dt>key</dt>
<dd>value</dd>
<dt>key</dt>
<dd>value</dd>
</dl>

I used <dl> <dt> <dd> and styled them with grid