Documentation comments in Swift use Markdown-flavored markup syntax. Swift doc comments utilize a full-fledged CommonMark parser library (known as [swift-cmark] in the Swift projects), which is rendered in Xcode QuickHelp.
Swift Markup syntax is exactly CommonMark, by design, not only for its straightforward implementation and completeness but also in the spirit of Markdown's readability through limited special syntax.
In addition to full Markdown support, the following extensions are supported via interpretation only after the CommonMark parser has finished with the doc comment block. These appear as list items at the top level of the comment's "document". The goal of these "extensions" was zero changes to the cmark library. Because they are regular list items, you may nest arbitrary content underneath them, such as multiple paragraphs, sublists, hyperlinks, etc. and they will be rendered in QuickHelp correctly.
All of the below extension "keywords" are matched without regard to case.
There are two methods of documenting parameters: a Parameters Section and
separate Parameter Fields. You can mix and match these forms as you see fit in
any order or continuity throughout the doc comment.
- Parameters:
- x: ...
- y: ...
- z: ...
- Parameter x: ...
- Parameter y: ...
This field documents the return value of a function or method. You may specify
multiple Returns items at the top level but only the last one will be
shown in Xcode's QuickHelp.
- Returns: ...
Functions that are marked as Throws should contain the following describing
what kind of errors are thrown and in what situations:
- Throws: ...
These extensions are also list items at the top level, which will also appear highlighted in Xcode QuickHelp as first-class citizens. Specifying more than one is supported and appear in order inside QuickHelp.
- Attention: ...
- Author: ...
- Authors: ...
- Bug: ...
- Complexity: ...
- Copyright: ...
- Date: ...
- Experiment: ...
- Important: ...
- Invariant: ...
- Note: ...
- Postcondition: ...
- Precondition: ...
- Remark: ...
- Remarks: ...
- Requires: ...
- See: ...
- Since: ...
- Todo: ...
- Version: ...
- Warning: ...
You can find more information on the visual effects of the documentation comments in Xcode's QuickHelp at the Markup Formatting Reference.