diff --git a/docs/src/test-api/class-testproject.md b/docs/src/test-api/class-testproject.md
index 5acda1ce41..cb6aea3618 100644
--- a/docs/src/test-api/class-testproject.md
+++ b/docs/src/test-api/class-testproject.md
@@ -138,7 +138,7 @@ You can configure entire test project to concurrently run all tests in all files
 * since: v1.10
 - type: ?<[RegExp]|[Array]<[RegExp]>>
 
-Filter to only run tests with a title matching one of the patterns. For example, passing `grep: /cart/` should only run tests with "cart" in the title. Also available globally and in the [command line](../test-cli.md) with the `-g` option.
+Filter to only run tests with a title matching one of the patterns. For example, passing `grep: /cart/` should only run tests with "cart" in the title. Also available globally and in the [command line](../test-cli.md) with the `-g` option. The regular expression will be tested against the string that consists of the test file name, `test.describe` name (if any) and the test name divided by spaces, e.g. `my-test.spec.ts my suite my test`.
 
 `grep` option is also useful for [tagging tests](../test-annotations.md#tag-tests).
 
diff --git a/packages/playwright-test/types/test.d.ts b/packages/playwright-test/types/test.d.ts
index 14314924b3..7b7242f5b0 100644
--- a/packages/playwright-test/types/test.d.ts
+++ b/packages/playwright-test/types/test.d.ts
@@ -184,7 +184,8 @@ export interface FullProject<TestArgs = {}, WorkerArgs = {}> {
   /**
    * Filter to only run tests with a title matching one of the patterns. For example, passing `grep: /cart/` should only
    * run tests with "cart" in the title. Also available globally and in the [command line](https://playwright.dev/docs/test-cli) with the `-g`
-   * option.
+   * option. The regular expression will be tested against the string that consists of the test file name,
+   * `test.describe` name (if any) and the test name divided by spaces, e.g. `my-test.spec.ts my suite my test`.
    *
    * `grep` option is also useful for [tagging tests](https://playwright.dev/docs/test-annotations#tag-tests).
    */
@@ -4649,7 +4650,8 @@ interface TestProject {
   /**
    * Filter to only run tests with a title matching one of the patterns. For example, passing `grep: /cart/` should only
    * run tests with "cart" in the title. Also available globally and in the [command line](https://playwright.dev/docs/test-cli) with the `-g`
-   * option.
+   * option. The regular expression will be tested against the string that consists of the test file name,
+   * `test.describe` name (if any) and the test name divided by spaces, e.g. `my-test.spec.ts my suite my test`.
    *
    * `grep` option is also useful for [tagging tests](https://playwright.dev/docs/test-annotations#tag-tests).
    */