Are the tables on top of some posts markdown or a feature?

It is a markdown table. It is part of the topic template.

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| :information_source: | **Summary** | ADD SHORT SUMMARY 
| :eyeglasses:|**Preview**| PREVIEW_LINK |
| :hammer_and_wrench:|**Repository**| REPOSITORY_LINK |
| :question:|**Install Guide**|[How to install a theme or theme component](https://meta.discourse.org/t/how-do-i-install-a-theme-or-theme-component/63682)|
| :open_book:|**New to Discourse Themes?**| [Beginner’s guide to using Discourse Themes](https://meta.discourse.org/t/beginners-guide-to-using-discourse-themes/91966)

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