diff --git a/docs/tint/layering.md b/docs/tint/layering.md
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+# Tint Source Layering
+
+The `BUILD.gn` is setup with small source units for various components
+in Tint. The hierarchy of sources almost matches to folder structure in
+tint (except for `base` which is a mix of things in `src/tint` and
+`src/tint/util`.
+
+
+```
++-----------------------------------------+
+|         Readers | Writers               |
++-----------------------------------------+
+                  |
+                  V
++-----------------------------------------+
+| Val | Demangler | Inspector | Transform |
++-----------------------------------------+
+   |              |
+   +--------------+------------------------------+
+                  |                              |
+                  V                              V
++-----------------------------------------+ +-----------+
+|                AST                      | |  Utils IO |
++-----------------------------------------+ +-----------+
+                  |                              |
+                  V                              |
++-----------------------------------------+      |
+|        Program  | Sem                   |      |
++-----------------------------------------+      |
+                  |                              |
+                  V                              |
++-----------------------------------------+      |
+|              AST Hdrs                   |      |
+|    (program and sem cause a cycle)      |      |
++-----------------------------------------+      |
+                  |                              |
+                  V                              |
++-----------------------------------------+      |
+|        Clone Context Hdrs               |      |
+|    (program and sem cause a cycle)      |      |
++-----------------------------------------+      |
+                  |                              |
+                  V                              |
++-----------------------------------------+      |
+|             Constant                    |      |
++-----------------------------------------+      |
+                  |                              |
+                  V                              |
++-----------------------------------------+      |
+|               Types                     |      |
++-----------------------------------------+      |
+                  |                              |
+                  V                              |
++-----------------------------------------+      |
+|              Builtin                    |      |
++-----------------------------------------+      |
+                  |                              |
+                  |------------------------------+
+                  V
++-----------------------------------------+
+|               Base                      |
++-----------------------------------------+
+                  |
+                  V
++-----------------------------------------+ +-------------+
+|            Text  (unicode)              | | Initializer |
++-----------------------------------------+ +-------------+
+```