For example, what type of Schema would something like Slim use?
The most relevant seems to be TechArticle but the actual usage of that type is very low (between 100 and 1000 domains).
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In the next level,
Article seems to be the most appropriate.
And from the sub-types of
Article, the type
TechArticle seems to be suitable:
A technical article - Example: How-to (task) topics, step-by-step, procedural troubleshooting, specifications, etc.
It even has a sub-type for an API reference:
Reference documentation for application programming interfaces (APIs).
For deciding which type to use, you should ignore the usage statistics. It’s irrelevant how often a type gets used in other documents if you need this type for your document. (Oh, and someone has to start, right?)
Besides that, the statistics include only a small subset of sites, and they get updated rarely.
And you’ll probably always find that the usage stats for types that are not connected with search engine features (like Rich Snippets) will be comparatively low.
You should use TechArticle schema, because it is most related to your framework website.
Don't count usage, because most of CMS like WordPress have plugin for news article, and Blogger.com by default using BlogPosting schema, and hence their usage are high.
As per my experience, I have seen only News Rich snippet in Search Result. All other schema like TechArticle, BlogPosting, ArticleBody did not display rich snippet in SERP, except the date(Time), that you want to display in search result.