diff --git a/docs/conf.py b/docs/conf.py
index dab953bf..199db8df 100644
--- a/docs/conf.py
+++ b/docs/conf.py
@@ -64,8 +64,8 @@ def create_constraints_inventory() -> None:
 api_target_substitutions: dict[str, str | tuple[str, str]] = {
     "EdgeType": "typing.TypeVar",
     "GraphEdgePropertyMap": ("obj", "qrules.argument_handling.GraphEdgePropertyMap"),
-    "GraphNodePropertyMap": ("obj", "qrules.argument_handling.GraphNodePropertyMap"),
     "GraphElementProperties": ("obj", "qrules.solving.GraphElementProperties"),
+    "GraphNodePropertyMap": ("obj", "qrules.argument_handling.GraphNodePropertyMap"),
     "GraphSettings": ("obj", "qrules.solving.GraphSettings"),
     "InitialFacts": ("obj", "qrules.combinatorics.InitialFacts"),
     "NewEdgeType": "typing.TypeVar",
@@ -75,6 +75,7 @@ def create_constraints_inventory() -> None:
     "ParticleWithSpin": ("obj", "qrules.particle.ParticleWithSpin"),
     "qrules.topology.EdgeType": "typing.TypeVar",
     "qrules.topology.NodeType": "typing.TypeVar",
+    "SpinFormalism": ("obj", "qrules.transition.SpinFormalism"),
     "StateDefinition": ("obj", "qrules.combinatorics.StateDefinition"),
     "TypeAlias": "typing.TypeAlias",
     "typing_extensions.TypeAlias": "typing.TypeAlias",
diff --git a/src/qrules/transition.py b/src/qrules/transition.py
index ec5443b4..59e683ae 100644
--- a/src/qrules/transition.py
+++ b/src/qrules/transition.py
@@ -88,6 +88,13 @@
     "canonical-helicity",
     "canonical",
 ]
+"""Name for the spin formalism to be used.
+
+The options :code:`"helicity"`, :code:`"canonical-helicity"`, and :code:`"canonical"`
+are all used for the helicity formalism, but :code:`"canonical-helicity"` and
+:code:`"canonical"` generate angular momentum and coupled spins as well on the
+interaction nodes.
+"""
 
 
 class SolvingMode(Enum):