The page at https://docs.expressionengine.com/latest/development/fieldtypes.html could use a massive refresh as well as the example fieldtype provided. I visited these several times while working on my new fieldtype and ended up needing to hit slack for help as these were lacking quite a bit. 3 needs a lot of attention,, but with 4 coming soon, they will probably need a refresher for it as well. 😉
ExpressionEngine implements Markdown Extra and BBCode. Please see the Markdown Extra docs and the BBCode Wikipedia article for a full reference.
**bold**, __bold__, *italics*, _italics_, ~strike/del~, `code()`
bold, italics, strike/del, code()
Link: [link title](https://example.com)
Image: 
[blockquote]...[/blockquote], [quote]...[/quote], and Markdown style:
> Some quoted text. > > This is all one quote.
[code]...[/code], and you can also specify the language for syntax highlighting, [code=php]...[/code]
GitHub flavored Markdown code fences are also supported:
```
public function decoderRing($str)
{
return str_rot13($str);
}
```