Accessibility: aria-posinset index starts illegally at zero on discussion list feed

[hollsk]

Current Behavior

Pull #3359 added useful aria Feed markup to discussion lists. The calculation that works out which number each item in the feed starts at has a small bug. The article count begins at zero instead of 1:

aria-posinset={pageNum * pageSize + itemNum}

Steps to Reproduce

You can see this in action by inspecting the HTML generated for the main discussion list at discuss.flarum.org:

<ul role="feed" class="DiscussionList-discussions">
    <li data-id="28506" role="article" aria-setsize="-1" aria-posinset="0">...</li>...
</ul>

Expected Behavior

Per the WAI-ARIA specification for this attribute, aria-posinset needs to start at 1:

Authors MUST set the value for aria-posinset to an integer greater than or equal to 1, and less than or equal to the size of the set when that size is known. Authors SHOULD use aria-setsize.

Screenshots

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Environment

• Flarum version: 1.8.9

Output of php flarum info

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Possible Solution

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Additional Context

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