Non-standard ARIA attributes do not work with `lwc:spread`

[Mr-VincentW]

Is your feature request related to a problem? Please describe. According to the LWC ARIA Reflection documentation, non-standard ARIA attributes are supported in LWC. This allows attributes like <a-comp aria-labelledby="a-label-id"></a-comp> to work as expected.

However, this is not the case when using lwc:spread, where non-standard aira attributes cause an "Unknown public property" error and are not applied.

i.e., this does not work:

• in HTML: <a-comp lwc:spread={props}></a-comp>
• in JS: props = { ariaLabelledBy: 'a-label-id' };

Describe the solution you'd like Ensure that lwc:spread supports non-standard ARIA attributes so that the behavior aligns with manually adding them one by one.

Additional context The issue occurs because non-standard ARIA attributes do not exist in the HTML element's property chain, leading to a validation failure at: https://github.com/salesforce/lwc/blob/62feccae9ae68baf2fb8a04c629550d99e1af6de/packages/%40lwc/engine-core/src/framework/modules/props.ts#L62

These tickets might be relevant:

• https://github.com/salesforce/lwc/issues/4545
• https://github.com/salesforce/lwc/issues/4425

[wjhsf]

Could you provide a playground link to reproduce the error? I've tried this and it seems to be rendering the attribute as expected.

[Mr-VincentW]

Hi,

Thanks for getting back to me.

Since this validation applies to the element where the attributes are set, the issue occurs only with native HTML elements, where non-standard ARIA attributes are not reflected.

In your test case, moving lwc:spread={props} to another native HTML element reproduces the issue. For example:

<template>
    <h1 id="h1">Used as ARIA label</h1>
    <section label="Labeled by heading" lwc:spread={props}>Section Content</section>
</template>

Cheers.