Add docs for HistoryEditor

docs/Summary.md

@@ -55,6 +55,7 @@
 - [Slate React](libraries/slate-react.md)
 - [Slate History](libraries/slate-history.md)
   - [History](/history/history.md)
+  - [HistoryEditor](/history/history-editor.md)
 - [Slate Hyperscript](libraries/slate-hyperscript.md)
 
 ## General

docs/history/history-editor.md

@@ -0,0 +1,78 @@
+# History Editor
+
+The `HistoryEditor` interface is added to the `Editor` when it is instantiated using the `withHistory` method.
+
+```typescript
+const [editor] = useState(() => withReact(withHistory(createEditor())))
+```
+
+This adds properties to `editor` that enables undo and redo to Slate.
+
+There are also a number of static methods to help while working with the Editor's undo/redo history.
+
+```typescript
+export interface HistoryEditor extends BaseEditor {
+  history: History
+  undo: () => void
+  redo: () => void
+  writeHistory: (stack: 'undos' | 'redos', batch: any) => void
+}
+```
+
+- [Static methods](history-editor.md#static-methods)
+  - [Undo and Redo](history-editor.md#undo-and-redo)
+  - [Merging and Saving](history-editor.md#merging-and-saving)
+  - [Check methods](history-editor.md#check-methods)
+- [Instance methods](history-editor.md#instance-methods)
+
+## Static methods
+
+### Undo and Redo
+
+#### `HistoryEditor.redo(editor: HistoryEditor): void`
+
+Redo to the previous saved state.
+
+#### `HistoryEditor.undo(editor: HistoryEditor): void`
+
+Undo to the previous saved state.
+
+### Merging and Savings
+
+#### `HistoryEditor.withoutMerging(editor: HistoryEditor, fn: () => void): void`
+
+Apply a series of changes inside a synchronous `fn`, without merging any of
+the new operations into previous save point in the history.
+
+#### `HistoryEditor.withoutSaving(editor: HistoryEditor, fn: () => void): void`
+
+Apply a series of changes inside a synchronous `fn`, without saving any of
+their operations into the history.
+
+### Check methods
+
+#### `HistoryEditor.isHistoryEditor(value: any): value is HistoryEditor`
+
+Check if a value is a `HistoryEditor` (i.e. it has the `HistoryEditor` interface).
+
+#### `HistoryEditor.isMerging(editor: HistoryEditor): boolean | undefined`
+
+Get the merge flag's current value.
+
+#### `HistoryEditor.isSaving(editor: HistoryEditor): boolean | undefined`
+
+Get the saving flag's current value.
+
+## Instance methods
+
+#### `undo(): void`
+
+Undo the last batch of operations
+
+#### `redo(): void`
+
+Redo the last undone batch of operations
+
+#### `writeHistory(stack: 'undos'| 'redos', batch: any) => void`
+
+Push a batch of operations as either `undos` or `redos` onto `editor.undos` or `editor.redos`