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diff --git a/doc/HOWTO.md b/doc/HOWTO.md
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--- a/doc/HOWTO.md
+++ b/doc/HOWTO.md
@@ -158,6 +158,44 @@ void test_example() {
 
 For low-level synth-only tests, you can still call `synth_init()` directly.
 
+## Auxiliary Texture Masking
+
+The project supports inter-effect texture sharing via the auxiliary texture registry. This allows effects to generate textures (masks, shadow maps, etc.) and make them available to other effects within the same frame.
+
+**Common use case:** Screen-space partitioning where different scenes render to complementary regions.
+
+```cpp
+class MaskGeneratorEffect : public Effect {
+  void init(MainSequence* demo) override {
+    demo_ = demo;
+    // Register a named auxiliary texture
+    demo->register_auxiliary_texture("my_mask", width_, height_);
+  }
+
+  void compute(WGPUCommandEncoder encoder, ...) override {
+    // Generate mask to auxiliary texture
+    WGPUTextureView mask_view = demo_->get_auxiliary_view("my_mask");
+    // ... render mask
+  }
+
+  void render(WGPURenderPassEncoder pass, ...) override {
+    // Use mask in scene rendering
+    WGPUTextureView mask_view = demo_->get_auxiliary_view("my_mask");
+    // ... render scene with mask
+  }
+};
+
+class MaskUserEffect : public Effect {
+  void render(WGPURenderPassEncoder pass, ...) override {
+    // Reuse mask from MaskGeneratorEffect
+    WGPUTextureView mask_view = demo_->get_auxiliary_view("my_mask");
+    // ... render scene with inverted mask
+  }
+};
+```
+
+See `doc/MASKING_SYSTEM.md` for detailed architecture and examples.
+
 ## Debugging
 
 ### Seeking / Fast-Forward