Add docs to layer API

src/ifcopenshell-python/ifcopenshell/api/layer/unassign_layer.py

@@ -16,18 +16,51 @@
 # You should have received a copy of the GNU Lesser General Public License
 # along with IfcOpenShell.  If not, see <http://www.gnu.org/licenses/>.
 
-import ifcopenshell
-
 
 class Usecase:
-    def __init__(self, file, **settings):
+    def __init__(self, file, item=None, layer=None):
+        """Unassigns an item from a layer
+
+        If the representation item isn't assigned to the layer, nothing will
+        happen.
+
+        :param item: An IfcRepresentationItem element to unassign
+        :type item: ifcopenshell.entity_instance.entity_instance
+        :param layer: The IfcPresentationLayerAssignment to unassign from
+        :type layer: ifcopenshell.entity_instance.entity_instance
+        :return: None
+        :rtype: None
+
+        Example::
+
+            # Remember, all geometry needs to specify the context it is part of first.
+            # See ifcopenshell.api.context.add_context for details.
+            model = ifcopenshell.api.run("context.add_context", model, context_type="Model")
+            body = ifcopenshell.api.run("context.add_context", model,
+                context_type="Model", context_identifier="Body", target_view="MODEL_VIEW", parent=model
+            )
+
+            wall = ifcopenshell.api.run("root.create_entity", model, ifc_class="IfcWall")
+            representation = ifcopenshell.api.run("geometry.add_wall_representation", model,
+                context=body, length=5, height=3, thickness=0.2)
+            ifcopenshell.api.run("geometry.assign_representation", model,
+                product=wall, representation=representation)
+
+            # Now let's create a layer that contains walls
+            layer = ifcopenshell.api.run("layer.add_layer", model, Name="AI-WALL")
+
+            # And assign our wall representation item (in this example, there is
+            # only one item) to the layer.
+            ifcopenshell.api.run("layer.assign_layer", model, item=representation.Items[0], layer=layer)
+
+            # Let's undo it!
+            ifcopenshell.api.run("layer.unassign_layer", model, item=representation.Items[0], layer=layer)
+        """
         self.file = file
         self.settings = {
-            "item": None,
-            "layer": None,
+            "item": item,
+            "layer": layer,
         }
-        for key, value in settings.items():
-            self.settings[key] = value
 
     def execute(self):
         assigned_items = set(self.settings["layer"].AssignedItems) or set()