Be more explicit about the equivalence between visibility labels and how they are expressed within package groups.
@@ -23,8 +23,12 @@ Each label has one of the following forms:
`__subpackages__` is special syntax.
* `"//foo/bar:my_package_group"`: Grants access to all of the packages named
- by the given [package group](be/functions.html#package_group). This can be
- used to allow access to an entire subtree, such as `//myproj/...`.
+ by the given [package group](be/functions.html#package_group).
+
+ * Package groups do not support the special `__pkg__` and
+ `__subpackages__` syntax. Within a package group, `"//foo/bar"` is
+ equivalent to `"//foo/bar:__pkg__"` and `"//foo/bar/..."` is equivalent
+ to `"//foo/bar:__subpackages__"`.
For example, if `//some/package:mytarget` has its `visibility` set to
`[":__subpackages__", "//tests:__pkg__"]`, then it could be used by any target
