High This Hint is very important, and definitely warrants attention. Issue This Hint represents an error or problem that needs to be fixed.

Contains duplicate element id values

This means that the URL in question contains DOM elements with duplicate id attribute values.

Why is this important?

Using duplicate id attribute values is invalid HTML, as HTML specification clearly states that attributes must be unique. Practically, most browsers can handle duplicate ids, but theoretically they can cause issues if the JavaScript is parsing or calling DOM elements based on these id values. Another issue is it can confuse Screen readers, as they use id values to expose a relationship between page elements.

What does the Hint check?

This Hint will trigger for any internal HTML URL that contains DOM elements with duplicate id attribute values.

Examples that trigger this Hint:

For example, the following HTML document contains two li elements with the same id:

<html>
<body>
<ul>
<li id="given-name">Jon Snow
<li id="given-name">Aegon Targaryen
</ul>
</body>

How do you resolve this issue?

Even if it may appear that browsers can handle pages with duplicate ids, there are lots of very good usability and accessibility reasons for using unique ids, so ensure that all duplicate ids are renamed to be unique and unambiguous. 

Further Reading

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