Fix typos in Extending docs

Author: krassowski

docs/Extending.ipynb

@@ -46,7 +46,7 @@
     "#### How to override the default implementation of a feature?\n",
     "\n",
     "You can specify a list of extensions to be disabled the the feature manager\n",
-    "passing their plugin identifiers in `superseds` field of `IFeatureOptions`."
+    "passing their plugin identifiers in `supersedes` field of `IFeatureOptions`."
    ]
   },
   {
@@ -64,7 +64,7 @@
     "\n",
     "#### Why virtual editor?\n",
     "\n",
-    "The vitual editor takes multiple instances of your editor (e.g. in a notebook)\n",
+    "The virtual editor takes multiple instances of your editor (e.g. in a notebook)\n",
     "and makes them act like a single editor. For example, when \"onKeyPress\" event is\n",
     "bound on the VirtualEditor instance, it should be bound onto each actual code\n",
     "editor; this allows the features to be implemented without the knowledge about\n",
@@ -89,7 +89,7 @@
     "`IDocumentWidget` interface. Each such widget has to adapted by a\n",
     "`WidgetAdapter` to enable its use with the LSP extension. The role of the\n",
     "`WidgetAdapter` is to extract the document metadata (language, mimetype) and the\n",
-    "underyling code editor (e.g. CodeMirror or Monaco) instances so that other parts\n",
+    "underlying code editor (e.g. CodeMirror or Monaco) instances so that other parts\n",
     "of the LSP extension can interface with them without knowing about the\n",
     "implementation details of the DocumentWidget (or even about the existence of a\n",
     "Notebook construct!).\n",
@@ -110,7 +110,7 @@
     "\n",
     "It is now possible to register custom code replacements using\n",
     "`ILSPCodeOverridesManager` token and to register custom foreign code extractors\n",
-    "using `ILSPCodeExtractorsManager` token, however this API is conssidered\n",
+    "using `ILSPCodeExtractorsManager` token, however this API is considered\n",
     "provisional and subject to change.\n",
     "\n",
     "#### Future plans for transclusions handling\n",
@@ -145,7 +145,7 @@
     "2. Prepare `CompletionKind` → `IconSvgString` mapping for the light (and\n",
     "   optionally dark) theme, implementing the `ICompletionIconSet` interface. We\n",
     "   have an additional `Kernel` completion kind that is used for completions\n",
-    "   provided by kernel that had no recognisable type provided.\n",
+    "   provided by kernel that had no recognizable type provided.\n",
     "\n",
     "3. Provide all other metadata required by the `ICompletionTheme` interface and\n",
     "   register it on `ILSPCompletionThemeManager` instance using `register_theme()`\n",
@@ -154,7 +154,7 @@
     "4. Provide any additional CSS styling targeting the JupyterLab completer\n",
     "   elements inside of `.lsp-completer-theme-{id}`, e.g.\n",
     "   `.lsp-completer-theme-material .jp-Completer-icon svg` for the material\n",
-    "   theme. Rememmber to include the styles by importing the in one of the source\n",
+    "   theme. Remember to include the styles by importing the in one of the source\n",
     "   files.\n",
     "\n",
     "For an example of a complete theme see\n",