diff --git a/src/Types.ts b/src/Types.ts
index 444c6e35ce..473e80c11b 100644
--- a/src/Types.ts
+++ b/src/Types.ts
@@ -98,6 +98,15 @@ export interface SubpieceModifier {
 export interface MatchingPairSymbolModifier {
   type: "matchingPairSymbol";
 }
+export interface LineNumberModifierPosition {
+  lineNumber: number;
+  isRelative: boolean;
+}
+export interface LineNumberModifier {
+  type: "lineNumber";
+  anchor: LineNumberModifierPosition;
+  active: LineNumberModifierPosition;
+}
 export interface IdentityModifier {
   type: "identity";
 }
@@ -109,11 +118,12 @@ export interface TailModifier {
 }
 
 export type Modifier =
+  | IdentityModifier
   | SurroundingPairModifier
   | ContainingScopeModifier
   | SubpieceModifier
   | MatchingPairSymbolModifier
-  | IdentityModifier
+  | LineNumberModifier
   | HeadModifier
   | TailModifier;
 
diff --git a/src/extension.ts b/src/extension.ts
index 1e28f5dea4..4147a6dfde 100644
--- a/src/extension.ts
+++ b/src/extension.ts
@@ -215,10 +215,38 @@ export async function activate(context: vscode.ExtensionContext) {
 
   addDecorationsDebounced();
 
+  function checkForEditsOutsideViewport(event: vscode.TextDocumentChangeEvent) {
+    const editor = vscode.window.activeTextEditor;
+    if (editor == null || editor.document !== event.document) {
+      return;
+    }
+    const { start, end } = editor.visibleRanges[0];
+    const ranges = [];
+    for (const edit of event.contentChanges) {
+      if (
+        edit.range.end.isBeforeOrEqual(start) ||
+        edit.range.start.isAfterOrEqual(end)
+      ) {
+        ranges.push(edit.range);
+      }
+    }
+    if (ranges.length > 0) {
+      ranges.sort((a, b) => a.start.line - b.start.line);
+      const linesText = ranges
+        .map((range) => `${range.start.line + 1}-${range.end.line + 1}`)
+        .join(", ");
+      vscode.window.showWarningMessage(
+        `Modification outside of viewport at lines: ${linesText}`
+      );
+    }
+  }
+
   function handleEdit(edit: vscode.TextDocumentChangeEvent) {
     graph.navigationMap.updateTokenRanges(edit);
 
     addDecorationsDebounced();
+
+    checkForEditsOutsideViewport(edit);
   }
 
   const recomputeDecorationStyles = async () => {
diff --git a/src/processTargets.ts b/src/processTargets.ts
index 48cf57662a..65da641791 100644
--- a/src/processTargets.ts
+++ b/src/processTargets.ts
@@ -14,6 +14,7 @@ import {
   Target,
   TypedSelection,
   Modifier,
+  LineNumberModifierPosition,
 } from "./Types";
 import { performInsideOutsideAdjustment } from "./performInsideOutsideAdjustment";
 import { SUBWORD_MATCHER } from "./constants";
@@ -370,6 +371,27 @@ function transformSelection(
       ];
     }
 
+    case "lineNumber": {
+      const getLine = (linePosition: LineNumberModifierPosition) =>
+        linePosition.isRelative
+          ? selection.editor.selection.active.line + linePosition.lineNumber
+          : linePosition.lineNumber;
+      return [
+        {
+          selection: update(selection, {
+            selection: () =>
+              new Selection(
+                getLine(modifier.anchor),
+                0,
+                getLine(modifier.active),
+                0
+              ),
+          }),
+          context: {},
+        },
+      ];
+    }
+
     case "matchingPairSymbol":
     case "surroundingPair":
       throw new Error("Not implemented");