switch_DotExpressionByOperation is used in two different cases: (a) from switch_sequence_operation_toSequence, where we do expect a DotExpression to become an expression that gives us a sequence, or at least try to use expression as is (we are going to apply a sequence op afterwards, so it's reasonable there would be smth like a sequence, provided model is valid); and (b), where any DotExpression is checked for being sequence operation (and might be not). There's no need for explicit copy in either case, but for (a) it's a 'last resort', try to use whatever DotExpression is there as sequence, rather than replacing it with a node SWITCH was attached to. For (b), there's no need to copy node explicitly, as DismissRule does the same, but much more effective (no sub-tree copying).
class_ConceptEditorDeclaration template from MAPPING_main does COPY-SRC for cellModel and assumes cellModel produces valid class members. template_EditorCellModel_CommonMethods (e.g. from CellModel_Collection) performs COPY-SRC for menuDescriptor.cellMenuPart, assuming there'd be templates that generate class members from menus. If MAPPING_CellMenu happens to be on another step, generation fails. Hence, rule MAPPING_main = MAPPING_CellMenu was added.