Discourse uses microdata ItemLists with ListItems in different places.
Some of these ListItems are only references/links to the actual object and do not represent an object by themselves. See ItemLists:
- Crawler-View: Category-View → “topic-list”
- Crawler-View: Topic-View → first post → “crawler-linkback-list”
Because these ListItems are only references, we can call the enclosing ItemLists a “summary”.
For a “summary” Google recommends to use a “simple” List:
See: Carousel (ItemList) Structured Data | Google Search Central | Documentation | Google for Developers
Google might see a “complex” ListItem with more properties set as an object for itself - thereby introducing new objects on the List-page instead of just referencing to the original object(-url).
e.g. Crawler-View: Category-View → “topic-list”
“complex” List - current state
<div itemscope="" itemtype="http://schema.org/ItemList">
<meta itemprop="itemListOrder" content="http://schema.org/ItemListOrderDescending">
<table class="topic-list">
[...]
<tbody class="topic-list-body">
[...]
<tr class="topic-list-item">
<td class="main-link topic-list-data" itemprop="itemListElement" itemscope="" itemtype="http://schema.org/ListItem">
<meta itemprop="name" content="Remove wrong structured data from every subpage – add "Sitelinks Search Box" to the homepage only">
<meta itemprop="url" content="https://meta.discourse.org/t/remove-wrong-structured-data-from-every-subpage-add-sitelinks-search-box-to-the-homepage-only/219299">
<meta itemprop="image" content="https://d11a6trkgmumsb.cloudfront.net/optimized/3X/6/8/68d84f5836ecc992fe21d08e05225eb57e47da38_2_1024x778.png">
<meta itemprop="position" content="2">
[...]
</tr>
[...]
</tbody>
</table>
</div>
“simple” List - pseudo code
<div itemscope="" itemtype="http://schema.org/ItemList">
<table class="topic-list">
[...]
<tbody class="topic-list-body">
[...]
<tr class="topic-list-item">
<td class="main-link topic-list-data" itemscope="" itemtype="http://schema.org/ListItem">
<meta itemprop="url" content="https://meta.discourse.org/t/remove-wrong-structured-data-from-every-subpage-add-sitelinks-search-box-to-the-homepage-only/219299">
<meta itemprop="position" content="2">
[...]
</tr>
[...]
</tbody>
</table>
</div>
