docs: documents the plugin behavior

docs/book/intro.md

@@ -18,3 +18,40 @@ use will have dependencies on legacy Zend Framework packages):
 ```bash
 $ composer remove laminas/laminas-dependency-plugin
 ```
+
+## What it does
+
+### zendframework and zfcampus packages listed in the composer.json
+
+For zendframework and zfcampus packages listed in the `composer.json` file, the
+plugin will identify the equivalent package from the Laminas Project, and
+slip-stream it in during when the user performs either a `composer install` or
+`composer update`.
+
+When this occurs, `composer show` will list the package installed. However, the
+`composer.json` will still list the zendframework or zfcampus package(s)
+originally present. To correct this situation, we recommend using the
+laminas-transfer `migrate` tooling.
+
+If you do not want this behavior, use the `--no-plugins` option when running
+your `composer install` or `composer update` operations.
+
+### zendframework and zfcampus packages requested via require operations
+
+When a user runs `composer require` and lists a zendframework or zfcampus
+package, the plugin will replace the package requested with the Laminas Project
+equivalent. The replacement package will both be installed as well as added to
+the `composer.json`.
+
+If you do not want this behavior, use the `--no-plugins` option when running
+your `composer require` operation.
+
+### zendframework and zfcampus packages installed as dependencies of other packages
+
+When a third-party package has dependencies on zendframework or zfcampus
+packages, the plugin will detect request for these packages and replace them
+with the Laminas Project equivalents prior to installation. Since these use the
+laminas-zendframework-bridge, all code should continue to work without issues.
+
+If you do not want this behavior, use the `--no-plugins` option when running
+your `composer require` operation.