What source comments does Xcode recognize as tags?

There is also MARK, FIXME, !!! and ???, e.g.

// FIXME: this bug needs to be fixed

and

// ???: WTF ???

You can see where these are defined in /Applications/Xcode.app/Contents/OtherFrameworks/XcodeEdit.framework/Versions/A/Resources/BaseSupport.xclangspec (or /Developer/Library/PrivateFrameworks/XcodeEdit.framework/Resources/BaseSupport.xclangspec for older versions of Xcode). Presumably you could also add your own tags here if you wanted to but I have not actually tried this. Here is the relevant section in BaseSupport.xclangspec:

{    Identifier = "xcode.lang.comment.mark";    Syntax = {        StartChars = "MTF!?";        Match = (            "^MARK:[ \t]+\(.*\)$",            "^\(TODO:[ \t]+.*\)$",       // include "TODO: " in the markers list            "^\(FIXME:[ \t]+.*\)$",      // include "FIXME: " in the markers list            "^\(!!!:.*\)$",              // include "!!!:" in the markers list            "^\(\\?\\?\\?:.*\)$"         // include "???:" in the markers list        );        // This is the order of captures. All of the match strings above need the same order.        CaptureTypes = (            "xcode.syntax.mark"        );        Type = "xcode.syntax.comment";    };},

These tags are also supported in the BBEdit text editor and its freeware sibling TextWrangler.

Looks like

// MARK:// TODO:// FIXME:// ???:// !!!:

all get translated into #pramga-like markers.

It appears that they stand for

// Mark, as in pragma// To Do note// Known bug marker// Serious question about form, content, or function// Serious concern about form, content, or function

You can use // MARK: - with tags below as per Apple example

// MARK: UICollectionViewDataSourcePrefetching    /// - Tag: Prefetching