There are many good options
Is there a list or a list of markdown options that work in TopAnswers?. I've seen in some comments that the options in this link work here https://markdown-it.github.io/, but I'm not sure if all of them work or just some of them.
Also, I saw that @Jack added the option to use a markdown for dbfiddle (which is great!), but I know this because I read the comment, so I think it should be good to have an updated list somewhere.
We are using [markdown-it](https://github.com/markdown-it/markdown-it), which:
* Has a useful [demo] page that you linked to in the question.
* Follows the [CommonMark] spec, except that on TopAnswers we ***[don't allow HTML input at all][safe]***, so no `<br>`, `sup` etc [that you can use on SE][sehtml][^pluginforhtml][^plugin].
* Isn't otherwise a radical departure from Markdown on SE, but there are a few more gotcha's such as:
1. Strikethrough in SE chat is `---strikethrough---` but CommonMark does not support strikethrough (however see below for our plugin support for `~~strikethrough~~`).
1. Markdown-it doesn't collapse adjacent blockquotes into a single blockquote:
> this is two
> this is a single
> blockquote with two paragraphs
1. Various other minor details from [this official CommonMark list][cmdiffs].
* Has some very sensible optional extensions (plugins) built-in — these are not part of the CommonMark spec but we have them switched on globally:
1. GitHub-style [strikethrough]
1. GitHub-style [tables]
* Has extensive support for other extensions, and we can add more or even create our own[^plugin].
* The following 'official'[^moreplugins] extensions are currently supported globally on TopAnswers:
1. [syntax highlighting][highlight][^syntax]
1. [definition lists][deflist]
* The following custom extensions are also currently supported globally:
* tweaking 'fuzzy' `dba.se` links to point to `dba.stackexchange.com`
* line numbers are available for fenced code blocks[^syntax] : ` ``` #`, or with a language, ` ``` apl #`, or to begin at a specified line number, ` ``` apl #3`
* Not actually a markdown plugin presently, but may be implemented as a plugin in future, and behaves similar to a plugin now:
* integration with [db<>fiddle], using this block level syntax:
[^pluginforhtml]: If you miss something that you can only do in with inline HTML on SE, it may be available as a plugin for markdown-it, or we can write our own.
[^plugin]: We'll need to be careful about adding non-standard syntax, but all requests for plugin support will be carefully considered — please ask here on meta for global support or with a meta question on the community site if it is site-specific like [MathML] or [Mathjax].
[^moreplugins]: There are a lot of other plugins, probably of widely varying quality and sanity, [listed on npm][npm]
[^syntax]: To chose a language for a code block, you need to use a [fenced code block](https://spec.commonmark.org/0.27/#fenced-code-blocks) and specify the language after the fence (e.g. `~~~none`, or the same with backticks ` ```none`)
[^supersub]: Note that spaces currently [need to be escaped](https://github.com/markdown-it/markdown-it-sup/issues/3) if you want to super/subscript multiple words (demo [here](https://markdown-it.github.io/#md3=%7B%22source%22%3A%22-%20not%20%5Eup%2C%20up%2C%20and%20away%5E%20%28%3D%20superscript%20ignored%29%5Cn-%20%26nbsp%3B%5Cn-%20but%20%5Eup%2C%5C%5C%20up%2C%5C%5C%20and%5C%5C%20away%5E%20%5Cn%5Cnor%20%5Cn%5Cn-%20not%20~swing%20low~%20%28%3D%20subscript%20ignored%29%5Cn-%20but%20~swing%5C%5C%20low~%22%2C%22defaults%22%3A%7B%22html%22%3Afalse%2C%22xhtmlOut%22%3Afalse%2C%22breaks%22%3Afalse%2C%22langPrefix%22%3A%22language-%22%2C%22linkify%22%3Atrue%2C%22typographer%22%3Atrue%2C%22_highlight%22%3Atrue%2C%22_strict%22%3Afalse%2C%22_view%22%3A%22html%22%7D%7D)).