HTML Guides for currency

The HTML specification defines a specific set of allowed attributes for each element. The <span> element supports global attributes (such as id, class, style, title, etc.) but does not recognize currency as a valid attribute. When you add a non-standard attribute like currency to an element, the W3C validator flags it because it doesn’t conform to the HTML standard.

This pattern often appears in e-commerce sites, financial applications, or internationalization contexts where developers want to associate a currency code (like USD, EUR, or GBP) with a price displayed in a <span>. While browsers will typically ignore unrecognized attributes without breaking the page, using them creates several problems:

• Standards compliance: Invalid HTML can lead to unpredictable behavior across different browsers and future browser versions.
• Maintainability: Other developers (or tools) won’t recognize non-standard attributes, making the codebase harder to understand and maintain.
• Accessibility: Assistive technologies rely on valid, well-structured HTML. Non-standard attributes may be ignored or misinterpreted.
• JavaScript interoperability: The HTMLElement.dataset API is specifically designed to work with data-* attributes, providing a clean and standard way to read custom data from elements.

The fix is straightforward: HTML provides the data-* attribute mechanism specifically for embedding custom data on elements. Any attribute prefixed with data- is valid on any HTML element, and its value is accessible in JavaScript via the element.dataset property.

Examples

❌ Invalid: Non-standard currency attribute

<span currency="USD">49.99</span>

This triggers the validation error because currency is not a recognized attribute for <span>.

✅ Fixed: Using a data-currency attribute

<span data-currency="USD">49.99</span>

The data-currency attribute is valid HTML. In JavaScript, you can access its value like this:

const span = document.querySelector('span');
console.log(span.dataset.currency); // "USD"

✅ Alternative: Using data-* with richer markup

If you need to convey more structured information, you can combine multiple data-* attributes:

<span class="price" data-currency="EUR" data-amount="29.99">€29.99</span>

✅ Alternative: Using microdata or structured markup

For SEO and machine-readable data, consider using established vocabularies like Schema.org:

<span itemscope itemtype="https://schema.org/MonetaryAmount">
  <meta itemprop="currency" content="USD">
  <span itemprop="value">49.99</span>
</span>

This approach provides semantic meaning that search engines and other consumers can understand, while remaining fully valid HTML.