Now provides PyTreeDef, and can detect PyTrees via issubclass(x, PyTree)

docs/api/advanced-features.md

@@ -1,13 +1,18 @@
 # Advanced features
 
-## Abstract base classes
+## Creating your own dtypes
 
 ::: jaxtyping.AbstractDtype
     selection:
         members:
             false
 
-::: jaxtyping.AbstractArray
-    selection:
-        members:
-            false
+## Introspection
+
+If you're writing your own type hint parser, then you may wish to detect if some Python object is a jaxtyping-provided type.
+
+You can check for dtypes by doing `issubclass(x, AbstractDtype)`. For example, `issubclass(Float32, AbstractDtype)` will pass.
+
+You can check for arrays by doing `issubclass(x, AbstractArray)`. Here, `AbstractArray` is the base class for all shape-and-dtype specified arrays, e.g. it's a base class for `Float32[Array, "foo"]`.
+
+You can check for pytrees by doing `issubclass(x, PyTree)`. For example, `issubclass(PyTree[int], PyTree)` will pass.

docs/api/pytree.md

@@ -5,4 +5,8 @@
         members:
             false
 
-Note that `jaxtyping.PyTree` is only available if JAX has been installed.
+`jaxtyping.PyTreeDef` is an alias for `jax.tree_util.PyTreeDef`, which is the type of the return from `jax.tree_util.tree_structure(...)`.
+
+:::jaxtyping.PyTreeDef
+
+Note that `jaxtyping.{PyTree, PyTreeDef}` are only available if JAX has been installed.