feat: overlays

docs/nixpkgs/multiple-nixpkgs.md

@@ -1,6 +1,6 @@
 # The Ingenious Uses of Multiple nixpkgs Instances
 
-In the section [Downgrade or Upgrade Packages](/nixos-with-flakes/downgrade-or-upgrade-packages.md), we have seen how to instantiate multiple distinct nixpkgs instances using the method `import nixpkgs {...}`. There are numerous applications for this technique, some common ones include:
+In the section [Downgrade or Upgrade Packages](../nixos-with-flakes/downgrade-or-upgrade-packages.md), we have seen how to instantiate multiple distinct nixpkgs instances using the method `import nixpkgs {...}`. There are numerous applications for this technique, some common ones include:
 
 1. Instantiate nixpkgs instances with different commit IDs to install various versions of software packages. This approach was used in the previous section [Downgrade or Upgrade Packages](/nixos-with-flakes/downgrade-or-upgrade-packages.md).
 

docs/nixpkgs/overlays.md

@@ -1,8 +1,10 @@
 # Overlays
 
-In the previous section, we learned about overriding derivations using the `override` function. 
+In the previous section, we learned about overriding derivations by `pkgs.xxx.override { ... }` or `pkgs.xxx.overrideAttrs (finalAttrs: previousAttrs: { ... });`.
-However, this approach will generate a new derivation and doesn't modify the original derivation in `pkgs` instance. 
+However, this approach will generate a new derivation and doesn't modify the original derivation in `pkgs` instance.
-To globally modify derivations in the detault `pkgs` instance, Nix provides a feature called "overlays".
+If the derivation you want to override is also used by other Nix packages, they will still use the unmodified derivation.
+
+To globally modify derivations in the detault nixpkgs instance, Nix provides a feature called "overlays".
 
 In traditional Nix environments, overlays can be configured globally using the `~/.config/nixpkgs/overlays.nix` or `~/.config/nixpkgs/overlays/*.nix` files. 
 However, with Flakes feature, to ensure system reproducibility, overlays cannot rely on configurations outside of the Git repository.

docs/zh/nixpkgs/overlays.md

@@ -1,6 +1,6 @@
 # Overlays
 
-前面介绍的 override 函数会生成一个新的 Derivation，因此它不会修改 pkgs 实例中原有的 Derivation，只适合作为局部参数使用。
+前面介绍的 `pkgs.xxx.override { ... }` 跟 `pkgs.xxx.overrideAttrs (finalAttrs: previousAttrs: { ... });` 都不会修改 pkgs 实例中原有的 Derivation，而是返回一个新的 Derivation，因此它们只适合作为局部参数使用。
 但如果你需要覆写的 Derivation 还被其他 Nix 包所依赖，那其他 Nix 包使用的仍然会是未被修改的 Derivation.
 
 为了解决这个问题，Nix 提供了 overlays 这个功能。