You can check your document for spelling mistakes. Serna comes with English spell-checking dictionaries only (US, GB, and Canadian), but you are free to add more dictionaries and specify the default one.
When you work with a document, it is possible to undo last several actions and then redo them if needed. All the actions together with document states are stored in memory consuming it, which may slow down Serna performance. To limit memory consumption, you can set the maximum depth of the undo/redo stack.