Update Composition doc.

Add specializes test USDA file.

doc/composition.md

@@ -1,31 +1,48 @@
 # subLayers
 
-* [ ] subLayers
-  * import scene
+import layer(USD)
 
 # inherits
 
-W.I.P.
-
-* [ ] `inherit`
-* [ ] `over`
+Inherit Prim in the layer
 
 # variantSets
 
-W.I.P.
-
 Works like `switch`.
 
-# references, payloads
+# references
 
-W.I.P.
+load layer(USD) from file(asset)
 
-payloads : delayed load
+# payloads
 
-# specializers
+delayed version of `references`
 
-Priority is low. Won't implement.
+# specializes
+
+Something like C++ template specialization.
+Override existing Prim
+(Note: `over` Prim spec cannot be used in same Layer(USD file), but can do it with specializes)
 
 ## References
 
 https://github.com/ColinKennedy/USD-Cookbook/blob/master/concepts/asset_composition_arcs.md
+
+
+## LIVRPS
+
+* Local: Load subLayer
+* Inherit: Resolve inherits
+  * Recursively apply LIVRP to target path(no Specializes evaluation)
+* Variants: Resolve VariantSets with currently selected Variants
+  * Recursively apply LIVRP to target layer(no Specializes evaulation)
+* References: Load references USD
+  * Recursively aply LIVRP to target layer(no Specializes evaulation)
+* Payload: Load payload USD
+  * Recursively aply LIVRP to target layer(no Specializes evaulation)
+* Specializes: Resolve specializes
+  * Recursively aply LIVRPS to target layer(do Specializes evaulation)
+
+  
+
+

tests/usda/specializes-002.usda

@@ -0,0 +1,21 @@
+#usda 1.0
+(
+    defaultPrim = "hello"
+)
+
+def Xform "hello"
+{
+  def Scope "Mats" 
+  {
+    def Material "Make"
+    {
+    }
+
+    def Material "CMake"
+    (
+      specializes = </hello/Mats/Make>
+    )
+    {
+    }
+  }
+}