diff --git a/src/lib/es2020.bigint.d.ts b/src/lib/es2020.bigint.d.ts
index f1f3282306136..22b1b6c3e4b55 100644
--- a/src/lib/es2020.bigint.d.ts
+++ b/src/lib/es2020.bigint.d.ts
@@ -223,7 +223,7 @@ interface BigInt64Array<TArrayBuffer extends ArrayBufferLike = ArrayBufferLike>
     includes(searchElement: bigint, fromIndex?: number): boolean;
 
     /**
-     * Returns the index of the first occurrence of a value in an array.
+     * Returns the index of the first occurrence of a value in an array, or -1 if it is not present.
      * @param searchElement The value to locate in the array.
      * @param fromIndex The array index at which to begin the search. If fromIndex is omitted, the
      * search starts at index 0.
@@ -241,7 +241,7 @@ interface BigInt64Array<TArrayBuffer extends ArrayBufferLike = ArrayBufferLike>
     keys(): ArrayIterator<number>;
 
     /**
-     * Returns the index of the last occurrence of a value in an array.
+     * Returns the index of the last occurrence of a value in an array, or -1 if it is not present.
      * @param searchElement The value to locate in the array.
      * @param fromIndex The array index at which to begin the search. If fromIndex is omitted, the
      * search starts at index 0.
@@ -514,7 +514,7 @@ interface BigUint64Array<TArrayBuffer extends ArrayBufferLike = ArrayBufferLike>
     includes(searchElement: bigint, fromIndex?: number): boolean;
 
     /**
-     * Returns the index of the first occurrence of a value in an array.
+     * Returns the index of the first occurrence of a value in an array, or -1 if it is not present.
      * @param searchElement The value to locate in the array.
      * @param fromIndex The array index at which to begin the search. If fromIndex is omitted, the
      * search starts at index 0.
@@ -532,7 +532,7 @@ interface BigUint64Array<TArrayBuffer extends ArrayBufferLike = ArrayBufferLike>
     keys(): ArrayIterator<number>;
 
     /**
-     * Returns the index of the last occurrence of a value in an array.
+     * Returns the index of the last occurrence of a value in an array, or -1 if it is not present.
      * @param searchElement The value to locate in the array.
      * @param fromIndex The array index at which to begin the search. If fromIndex is omitted, the
      * search starts at index 0.
diff --git a/src/lib/es5.d.ts b/src/lib/es5.d.ts
index 3ca96f12760be..f593fd3c1e342 100644
--- a/src/lib/es5.d.ts
+++ b/src/lib/es5.d.ts
@@ -412,14 +412,14 @@ interface String {
     concat(...strings: string[]): string;
 
     /**
-     * Returns the position of the first occurrence of a substring.
+     * Returns the position of the first occurrence of a substring, or -1 if it is not present.
      * @param searchString The substring to search for in the string
      * @param position The index at which to begin searching the String object. If omitted, search starts at the beginning of the string.
      */
     indexOf(searchString: string, position?: number): number;
 
     /**
-     * Returns the last occurrence of a substring in the string.
+     * Returns the last occurrence of a substring in the string, or -1 if it is not present.
      * @param searchString The substring to search for.
      * @param position The index at which to begin searching. If omitted, the search begins at the end of the string.
      */
@@ -1955,7 +1955,7 @@ interface Int8Array<TArrayBuffer extends ArrayBufferLike = ArrayBufferLike> {
     forEach(callbackfn: (value: number, index: number, array: this) => void, thisArg?: any): void;
 
     /**
-     * Returns the index of the first occurrence of a value in an array.
+     * Returns the index of the first occurrence of a value in an array, or -1 if it is not present.
      * @param searchElement The value to locate in the array.
      * @param fromIndex The array index at which to begin the search. If fromIndex is omitted, the
      * search starts at index 0.
@@ -1970,7 +1970,7 @@ interface Int8Array<TArrayBuffer extends ArrayBufferLike = ArrayBufferLike> {
     join(separator?: string): string;
 
     /**
-     * Returns the index of the last occurrence of a value in an array.
+     * Returns the index of the last occurrence of a value in an array, or -1 if it is not present.
      * @param searchElement The value to locate in the array.
      * @param fromIndex The array index at which to begin the search. If fromIndex is omitted, the
      * search starts at index 0.
@@ -2237,7 +2237,7 @@ interface Uint8Array<TArrayBuffer extends ArrayBufferLike = ArrayBufferLike> {
     forEach(callbackfn: (value: number, index: number, array: this) => void, thisArg?: any): void;
 
     /**
-     * Returns the index of the first occurrence of a value in an array.
+     * Returns the index of the first occurrence of a value in an array, or -1 if it is not present.
      * @param searchElement The value to locate in the array.
      * @param fromIndex The array index at which to begin the search. If fromIndex is omitted, the
      * search starts at index 0.
@@ -2252,7 +2252,7 @@ interface Uint8Array<TArrayBuffer extends ArrayBufferLike = ArrayBufferLike> {
     join(separator?: string): string;
 
     /**
-     * Returns the index of the last occurrence of a value in an array.
+     * Returns the index of the last occurrence of a value in an array, or -1 if it is not present.
      * @param searchElement The value to locate in the array.
      * @param fromIndex The array index at which to begin the search. If fromIndex is omitted, the
      * search starts at index 0.
@@ -2519,7 +2519,7 @@ interface Uint8ClampedArray<TArrayBuffer extends ArrayBufferLike = ArrayBufferLi
     forEach(callbackfn: (value: number, index: number, array: this) => void, thisArg?: any): void;
 
     /**
-     * Returns the index of the first occurrence of a value in an array.
+     * Returns the index of the first occurrence of a value in an array, or -1 if it is not present.
      * @param searchElement The value to locate in the array.
      * @param fromIndex The array index at which to begin the search. If fromIndex is omitted, the
      * search starts at index 0.
@@ -2534,7 +2534,7 @@ interface Uint8ClampedArray<TArrayBuffer extends ArrayBufferLike = ArrayBufferLi
     join(separator?: string): string;
 
     /**
-     * Returns the index of the last occurrence of a value in an array.
+     * Returns the index of the last occurrence of a value in an array, or -1 if it is not present.
      * @param searchElement The value to locate in the array.
      * @param fromIndex The array index at which to begin the search. If fromIndex is omitted, the
      * search starts at index 0.
@@ -2800,7 +2800,7 @@ interface Int16Array<TArrayBuffer extends ArrayBufferLike = ArrayBufferLike> {
      */
     forEach(callbackfn: (value: number, index: number, array: this) => void, thisArg?: any): void;
     /**
-     * Returns the index of the first occurrence of a value in an array.
+     * Returns the index of the first occurrence of a value in an array, or -1 if it is not present.
      * @param searchElement The value to locate in the array.
      * @param fromIndex The array index at which to begin the search. If fromIndex is omitted, the
      * search starts at index 0.
@@ -2815,7 +2815,7 @@ interface Int16Array<TArrayBuffer extends ArrayBufferLike = ArrayBufferLike> {
     join(separator?: string): string;
 
     /**
-     * Returns the index of the last occurrence of a value in an array.
+     * Returns the index of the last occurrence of a value in an array, or -1 if it is not present.
      * @param searchElement The value to locate in the array.
      * @param fromIndex The array index at which to begin the search. If fromIndex is omitted, the
      * search starts at index 0.
@@ -3082,7 +3082,7 @@ interface Uint16Array<TArrayBuffer extends ArrayBufferLike = ArrayBufferLike> {
     forEach(callbackfn: (value: number, index: number, array: this) => void, thisArg?: any): void;
 
     /**
-     * Returns the index of the first occurrence of a value in an array.
+     * Returns the index of the first occurrence of a value in an array, or -1 if it is not present.
      * @param searchElement The value to locate in the array.
      * @param fromIndex The array index at which to begin the search. If fromIndex is omitted, the
      * search starts at index 0.
@@ -3097,7 +3097,7 @@ interface Uint16Array<TArrayBuffer extends ArrayBufferLike = ArrayBufferLike> {
     join(separator?: string): string;
 
     /**
-     * Returns the index of the last occurrence of a value in an array.
+     * Returns the index of the last occurrence of a value in an array, or -1 if it is not present.
      * @param searchElement The value to locate in the array.
      * @param fromIndex The array index at which to begin the search. If fromIndex is omitted, the
      * search starts at index 0.
@@ -3363,7 +3363,7 @@ interface Int32Array<TArrayBuffer extends ArrayBufferLike = ArrayBufferLike> {
     forEach(callbackfn: (value: number, index: number, array: this) => void, thisArg?: any): void;
 
     /**
-     * Returns the index of the first occurrence of a value in an array.
+     * Returns the index of the first occurrence of a value in an array, or -1 if it is not present.
      * @param searchElement The value to locate in the array.
      * @param fromIndex The array index at which to begin the search. If fromIndex is omitted, the
      * search starts at index 0.
@@ -3378,7 +3378,7 @@ interface Int32Array<TArrayBuffer extends ArrayBufferLike = ArrayBufferLike> {
     join(separator?: string): string;
 
     /**
-     * Returns the index of the last occurrence of a value in an array.
+     * Returns the index of the last occurrence of a value in an array, or -1 if it is not present.
      * @param searchElement The value to locate in the array.
      * @param fromIndex The array index at which to begin the search. If fromIndex is omitted, the
      * search starts at index 0.
@@ -3644,7 +3644,7 @@ interface Uint32Array<TArrayBuffer extends ArrayBufferLike = ArrayBufferLike> {
      */
     forEach(callbackfn: (value: number, index: number, array: this) => void, thisArg?: any): void;
     /**
-     * Returns the index of the first occurrence of a value in an array.
+     * Returns the index of the first occurrence of a value in an array, or -1 if it is not present.
      * @param searchElement The value to locate in the array.
      * @param fromIndex The array index at which to begin the search. If fromIndex is omitted, the
      * search starts at index 0.
@@ -3659,7 +3659,7 @@ interface Uint32Array<TArrayBuffer extends ArrayBufferLike = ArrayBufferLike> {
     join(separator?: string): string;
 
     /**
-     * Returns the index of the last occurrence of a value in an array.
+     * Returns the index of the last occurrence of a value in an array, or -1 if it is not present.
      * @param searchElement The value to locate in the array.
      * @param fromIndex The array index at which to begin the search. If fromIndex is omitted, the
      * search starts at index 0.
@@ -3926,7 +3926,7 @@ interface Float32Array<TArrayBuffer extends ArrayBufferLike = ArrayBufferLike> {
     forEach(callbackfn: (value: number, index: number, array: this) => void, thisArg?: any): void;
 
     /**
-     * Returns the index of the first occurrence of a value in an array.
+     * Returns the index of the first occurrence of a value in an array, or -1 if it is not present.
      * @param searchElement The value to locate in the array.
      * @param fromIndex The array index at which to begin the search. If fromIndex is omitted, the
      * search starts at index 0.
@@ -3941,7 +3941,7 @@ interface Float32Array<TArrayBuffer extends ArrayBufferLike = ArrayBufferLike> {
     join(separator?: string): string;
 
     /**
-     * Returns the index of the last occurrence of a value in an array.
+     * Returns the index of the last occurrence of a value in an array, or -1 if it is not present.
      * @param searchElement The value to locate in the array.
      * @param fromIndex The array index at which to begin the search. If fromIndex is omitted, the
      * search starts at index 0.
@@ -4208,7 +4208,7 @@ interface Float64Array<TArrayBuffer extends ArrayBufferLike = ArrayBufferLike> {
     forEach(callbackfn: (value: number, index: number, array: this) => void, thisArg?: any): void;
 
     /**
-     * Returns the index of the first occurrence of a value in an array.
+     * Returns the index of the first occurrence of a value in an array, or -1 if it is not present.
      * @param searchElement The value to locate in the array.
      * @param fromIndex The array index at which to begin the search. If fromIndex is omitted, the
      * search starts at index 0.
@@ -4223,7 +4223,7 @@ interface Float64Array<TArrayBuffer extends ArrayBufferLike = ArrayBufferLike> {
     join(separator?: string): string;
 
     /**
-     * Returns the index of the last occurrence of a value in an array.
+     * Returns the index of the last occurrence of a value in an array, or -1 if it is not present.
      * @param searchElement The value to locate in the array.
      * @param fromIndex The array index at which to begin the search. If fromIndex is omitted, the
      * search starts at index 0.
diff --git a/tests/baselines/reference/completionsStringMethods.baseline b/tests/baselines/reference/completionsStringMethods.baseline
index 3935df481ea3b..e7e9cf31bfbdc 100644
--- a/tests/baselines/reference/completionsStringMethods.baseline
+++ b/tests/baselines/reference/completionsStringMethods.baseline
@@ -443,7 +443,7 @@
           ],
           "documentation": [
             {
-              "text": "Returns the position of the first occurrence of a substring.",
+              "text": "Returns the position of the first occurrence of a substring, or -1 if it is not present.",
               "kind": "text"
             }
           ],
@@ -585,7 +585,7 @@
           ],
           "documentation": [
             {
-              "text": "Returns the last occurrence of a substring in the string.",
+              "text": "Returns the last occurrence of a substring in the string, or -1 if it is not present.",
               "kind": "text"
             }
           ],