Add pub(restricted) docs

src/visibility-and-privacy.md

@@ -134,6 +134,67 @@ For a Rust program to pass the privacy checking pass, all paths must be valid
 accesses given the two rules above. This includes all use statements,
 expressions, types, etc.
 
+## `pub(in path)`, `pub(crate)`, `pub(super)`, and `pub(self)`
+
+In addition to public and private, Rust allows users to declare an item as
+visible within a given scope. The rules for `pub` restrictions are as follows:
+- `pub(in path)` makes an item visible within the provided `path`. `path` must
+be a parent module of the item whose visibility is being declared.
+- `pub(crate)` makes an item visible within the current crate.
+- `pub(super)` makes an item visible to the parent module. This equivalent to
+`pub(in super)`.
+- `pub(self)` makes an item visible to the current module. This is equivalent
+to `pub(in self)`.
+
+Here's an example:
+
+```rust
+pub mod outer_mod {
+    pub mod inner_mod {
+        // This function is visible within `outer_mod`
+        pub(in outer_mod) fn outer_mod_visible_fn() {}
+
+        // This function is visible to the entire crate
+        pub(crate) fn crate_visible_fn() {}
+
+        // This function is visible within `outer_mod`
+        pub(super) fn super_mod_visible_fn() {
+            // This function is visible since we're in the same `mod`
+            inner_mod_visible_fn();
+        }
+
+        // This function is visible
+        pub(self) fn inner_mod_visible_fn() {}
+    }
+    pub fn foo() {
+        inner_mod::outer_mod_visible_fn();
+        inner_mod::crate_visible_fn();
+        inner_mod::super_mod_visible_fn();
+
+        // This function is no longer visible since we're outside of `inner_mod`
+        // Error! `inner_mod_visible_fn` is private
+        //inner_mod::inner_mod_visible_fn();
+    }
+}
+
+fn bar() {
+    // This function is still visible since we're in the same crate
+    outer_mod::inner_mod::crate_visible_fn();
+
+    // This function is no longer visible since we're outside of `outer_mod`
+    // Error! `super_mod_visible_fn` is private
+    //outer_mod::inner_mod::super_mod_visible_fn();
+
+    // This function is no longer visible since we're outside of `outer_mod`
+    // Error! `outer_mod_visible_fn` is private
+    //outer_mod::inner_mod::outer_mod_visible_fn();
+
+    outer_mod::foo();
+}
+
+fn main() { bar() }
+```
+
 ## Re-exporting and Visibility
 
 Rust allows publicly re-exporting items through a `pub use` directive. Because