Write documentation for structural API module

src/ifcopenshell-python/ifcopenshell/api/structural/add_structural_load_case.py

@@ -20,23 +20,36 @@ import ifcopenshell.api
 
 
 class Usecase:
-    def __init__(self, file, **settings):
+    def __init__(
+        self, file, name="Unnamed", action_type="NOTDEFINED", action_source="NOTDEFINED"
+    ):
+        """Adds a new load case, which is a collection of related load groups
+
+        :param name: The name of the load case
+        :type name: str
+        :param action_type: Choose from EXTRAORDINARY_A, PERMANENT_G,
+            or VARIABLE_Q, taken from the Eurocode standard.
+        :type action_type: str
+        :param action_source: The source of the load case, such as DEAD_LOAD_G,
+            LIVE_LOAD_Q, TRANSPORT, ICE, etc. For the full list consult
+            IfcActionSourceTypeEnum in the IFC documentation.
+        :type action_source: str
+        :return: The new IfcStructuralLoadCase
+        :rtype: ifcopenshell.entity_instance.entity_instance
+        """
         self.file = file
         self.settings = {
-            "name": "Unnamed",
-            "predefined_type": "LOAD_CASE",
-            "action_type": "NOTDEFINED",
-            "action_source": "NOTDEFINED",
+            "name": name,
+            "action_type": action_type,
+            "action_source": action_source,
         }
-        for key, value in settings.items():
-            self.settings[key] = value
 
     def execute(self):
         load_case = ifcopenshell.api.run(
             "root.create_entity",
             self.file,
             ifc_class="IfcStructuralLoadCase",
-            predefined_type=self.settings["predefined_type"],
+            predefined_type="LOAD_CASE",
             name=self.settings["name"],
         )
         load_case.ActionType = self.settings["action_type"]