diff --git a/README.md b/README.md
index de89bbf..7736440 100644
--- a/README.md
+++ b/README.md
@@ -1,3 +1,41 @@
 # ⌨️ Development Containers goodies
 
 > A development container (or dev container for short) allows you to use a container as a full-featured development environment. It can be used to run an application, to separate tools, libraries, or runtimes needed for working with a codebase, and to aid in continuous integration and testing. Dev containers can be run locally or remotely, in a private or public cloud, in a variety of supporting tools and editors. - https://containers.dev
+
+## Install PHP extensions
+
+The `install-php-extensions` feature installs PHP extensions. Set `extensions` to names separated by spaces or commas, for example `zip` or `zip, gd`.
+
+Official images from https://hub.docker.com/_/php provide `docker-php-ext-install`, `docker-php-ext-configure`, `docker-php-ext-enable`, and `docker-php-source`. On those images the feature runs [mlocati/docker-php-extension-installer](https://github.com/mlocati/docker-php-extension-installer) 2.2.5.
+
+Debian and Ubuntu images such as `mcr.microsoft.com/devcontainers/base` do not provide those commands. On those images the feature installs `php-cli` and the distro package for each extension. `zip` installs `php-zip`. Apt repositories from the image choose the PHP version.
+
+Official PHP image:
+
+```json
+{
+  "image": "php:8.3-cli",
+  "features": {
+    "ghcr.io/opencodeco/devcontainers/install-php-extensions": {
+      "extensions": "zip"
+    }
+  }
+}
+```
+
+Debian or Ubuntu image:
+
+```json
+{
+  "image": "mcr.microsoft.com/devcontainers/base:bullseye",
+  "features": {
+    "ghcr.io/opencodeco/devcontainers/install-php-extensions": {
+      "extensions": "zip"
+    }
+  }
+}
+```
+
+Any other image fails before mlocati/docker-php-extension-installer is downloaded. The error names both supported bases.
+
+See [features/install-php-extensions/README.md](features/install-php-extensions/README.md).
diff --git a/features/install-php-extensions/README.md b/features/install-php-extensions/README.md
index 5bec7be..c54b201 100644
--- a/features/install-php-extensions/README.md
+++ b/features/install-php-extensions/README.md
@@ -14,7 +14,22 @@ Any other image stops before that installer is downloaded. The error names both
 
 `extensions` is a string of extension names separated by spaces or commas. Example: `zip` or `zip, gd`.
 
-## Example
+## Examples
+
+Official PHP image:
+
+```json
+{
+  "image": "php:8.3-cli",
+  "features": {
+    "ghcr.io/opencodeco/devcontainers/install-php-extensions": {
+      "extensions": "zip"
+    }
+  }
+}
+```
+
+Debian or Ubuntu image:
 
 ```json
 {