HTML Guides for duplicate

Within a <dl>, each name should appear in only one <dt>, so a term with several values gets one <dt> followed by several <dd> elements.

A description list is a set of name-value groups, and the HTML specification says a single <dl> should not have more than one <dt> for each name. When the same term shows up twice with different values, readers can't tell whether the second entry replaces the first, adds to it, or is a mistake. Repeated terms often come from lists built from data, such as product specifications where one attribute is output twice.

The validator compares the text content of each <dt>. It ignores markup and leading or trailing whitespace, so <dt><b>Size</b></dt> and <dt> Size </dt> both count as Size. The comparison is case-sensitive, so Size and size are different names. Wrapping each group in a <div> doesn't help, because the check covers the whole <dl>. Along with this warning, the validator adds a second message pointing to the first <dt> with that name.

If both values belong to the same term, keep one <dt> and put each value in its own <dd>. If the entries describe different things that share a label, give each <dt> a distinct name, or move them into separate <dl> elements, since the rule applies only within a single list.

Invalid example

<dl>

<dt>Size</dt>

<dd>Small</dd>

<dt>Color</dt>

<dd>Red</dd>

<dt>Size</dt>

<dd>Medium</dd>

</dl>

Valid example

<dl>

<dt>Size</dt>

<dd>Small</dd>

<dd>Medium</dd>

<dt>Color</dt>

<dd>Red</dd>

</dl>

Valid example with distinct names

<dl>

<dt>Net weight</dt>

<dd>1.2 kg</dd>

<dt>Gross weight</dt>

<dd>1.4 kg</dd>

</dl>

This message points to the first <dt> in a <dl> whose name is repeated later in the same list.

It always comes with a duplicate dt name warning on the later <dt>. Together, the two messages show where each copy of the term is, so you can compare them and decide which one to keep. The HTML specification says a single <dl> should not have more than one <dt> for each name.

The validator compares the text content of each <dt>. It ignores markup and leading or trailing whitespace, so <dt><b>Size</b></dt> and <dt>Size</dt> have the same name. The comparison is case-sensitive, so Size and size don't clash.

The first <dt> is usually fine on its own; the fix goes where the name repeats. If both entries describe the same term, keep one <dt> and give each value its own <dd>. If they describe different things, give each <dt> a distinct name. Once every name in the list is unique, both messages go away.

Invalid example

<dl>

<dt>Size</dt>

<dd>Small</dd>

<dt>Color</dt>

<dd>Red</dd>

<dt>Size</dt>

<dd>Medium</dd>

</dl>

Valid example

<dl>

<dt>Size</dt>

<dd>Small</dd>

<dd>Medium</dd>

<dt>Color</dt>

<dd>Red</dd>

</dl>