distinguish language and library processes more consistently

Author: jyn514

src/SUMMARY.md

@@ -41,7 +41,7 @@
 - [Mastering @rustbot](./rustbot.md)
 - [Walkthrough: a typical contribution](./walkthrough.md)
 - [Procedures for Breaking Changes](./bug-fix-procedure.md)
-- [Implementing new features](./implementing_new_features.md)
+- [Implementing new language features](./implementing_new_features.md)
 - [Stability attributes](./stability.md)
 - [Stabilizing Features](./stabilization_guide.md)
 - [Feature Gates](./feature-gates.md)

src/implementing_new_features.md

@@ -1,11 +1,16 @@
-# Implementing new features
+# Implementing new language features
 
 <!-- toc -->
 
 When you want to implement a new significant feature in the compiler,
 you need to go through this process to make sure everything goes
 smoothly.
 
+**NOTE: this section is for *language* features, not *library* features, which use [a different
+*process].**
+
+[a different process]: ./stability.md
+
 ## The @rfcbot FCP process
 
 When the change is small and uncontroversial, then it can be done

src/stability.md

@@ -1,12 +1,12 @@
 # Stability attributes
 
-<!-- toc -->
-
 This section is about the stability attributes and schemes that allow stable
 APIs to use unstable APIs internally in the rustc standard library.
 
-For instructions on stabilizing a language feature see [Stabilizing
-Features](./stabilization_guide.md).
+**NOTE**: this section is for *library* features, not *language* features. For instructions on
+stabilizing a language feature see [Stabilizing Features](./stabilization_guide.md).
+
+<!-- toc -->
 
 ## unstable
 

src/stabilization_guide.md

@@ -1,6 +1,6 @@
 # Request for stabilization
 
-**NOTE**: this page is about stabilizing language features.
+**NOTE**: this page is about stabilizing *language* features.
 For stabilizing *library* features, see [Stabilizing a library feature].
 
 [Stabilizing a library feature]: ./stability.md#stabilizing-a-library-feature