By default the "Select container" button in the spatial decomposition panel clears current selection before selecting the container. Shift + Click adds the container to selection, ALT + Click removes the container from selection. Added tooltip to the button for keypresses.

src/bonsai/bonsai/bim/module/spatial/operator.py

@@ -159,7 +159,18 @@ class SelectContainer(bpy.types.Operator, tool.Ifc.Operator):
     bl_idname = "bim.select_container"
     bl_label = "Select Container"
     bl_options = {"REGISTER", "UNDO"}
+    bl_description = "SHIFT + Click to add container to selection\nALT + Click to remove container from selection"
     container: bpy.props.IntProperty()
+    selection_mode: bpy.props.EnumProperty(items=[["ADD"] * 3, ["REMOVE"] * 3, ["SINGLE" * 3]])
+
+    def invoke(self, context, event):
+        if event.shift:
+            self.selection_mode = "ADD"
+        elif event.alt:
+            self.selection_mode = "REMOVE"
+        else:
+            self.selection_mode = "SINGLE"
+        return self.execute(context)
 
     def _execute(self, context):
         if self.container:
@@ -169,7 +180,12 @@ class SelectContainer(bpy.types.Operator, tool.Ifc.Operator):
         else:
             return
         if container:
-            core.select_container(tool.Ifc, tool.Spatial, container=container)
+            core.select_container(
+                tool.Ifc,
+                tool.Spatial,
+                container=container,
+                selection_mode=self.selection_mode,
+            )
 
 
 class SelectSimilarContainer(bpy.types.Operator, tool.Ifc.Operator):

src/bonsai/bonsai/core/spatial.py

@@ -101,8 +101,10 @@ def copy_to_container(
     return result_objs
 
 
-def select_container(ifc: tool.Ifc, spatial: tool.Spatial, container: ifcopenshell.entity_instance) -> None:
-    spatial.set_active_object(ifc.get_object(container))
+def select_container(
+    ifc: tool.Ifc, spatial: tool.Spatial, container: ifcopenshell.entity_instance, selection_mode: str = "ADD"
+) -> None:
+    spatial.set_active_object(ifc.get_object(container), selection_mode=selection_mode)
 
 
 def select_similar_container(ifc: tool.Ifc, spatial: tool.Spatial, obj: bpy.types.Object) -> None:

src/bonsai/bonsai/tool/blender.py

@@ -515,12 +515,22 @@ class Blender(bonsai.core.tool.Blender):
         active_object.select_set(True)
 
     @classmethod
-    def select_object(cls, obj: bpy.types.Object):
+    def set_object_selection(cls, obj: bpy.types.Object, state: bool = True):
         try:
-            obj.select_set(True)
+            obj.select_set(state)
         except RuntimeError:  # Trying to select a hidden object throws an error
             pass
 
+    @classmethod
+    def select_object(cls, obj: bpy.types.Object):
+        cls.set_object_selection(obj, True)
+
+    @classmethod
+    def deselect_object(cls, obj: bpy.types.Object, ensure_active_object: bool = True):
+        cls.set_object_selection(obj, False)
+        if ensure_active_object and bpy.context.view_layer.objects.active == obj and bpy.context.selected_objects:
+            cls.set_active_object(bpy.context.selected_objects[-1])
+
     @classmethod
     def set_objects_selection(
         cls,

src/bonsai/bonsai/tool/spatial.py

@@ -131,8 +131,13 @@ class Spatial(bonsai.core.tool.Spatial):
         tool.Blender.select_object(obj)
 
     @classmethod
-    def set_active_object(cls, obj: bpy.types.Object) -> None:
-        tool.Blender.set_active_object(obj)
+    def set_active_object(cls, obj: bpy.types.Object, selection_mode: str = "ADD") -> None:
+        if selection_mode == "ADD":
+            tool.Blender.set_active_object(obj)
+        elif selection_mode == "REMOVE":
+            tool.Blender.deselect_object(obj)
+        else:
+            tool.Blender.select_and_activate_single_object(bpy.context, obj)
 
     @classmethod
     def set_relative_object_matrix(