Add documentation

docs/integrations/plugins.md

@@ -0,0 +1,29 @@
+Pydantic allows users to create plugins that can be used to extend the functionality of the library.
+
+Plugins are installed via Python entry points. You can read more about entry points in the
+[Entry points specification](https://packaging.python.org/specifications/entry-points/) from the
+Python Packaging Authority.
+
+In case you have a project called `pydantic-plugin`, you can create a plugin by adding the following
+to your `pyproject.toml`:
+
+```toml
+[project.entry-points.pydantic]
+pydantic_plugin = "pydantic_plugin:plugin"
+```
+
+The entry point group is `pydantic`, and the name of the entry point is the name of the plugin.
+
+Plugins are loaded in the order they are found, and the order they are found is not guaranteed.
+
+Consider that you have a plugin called `pydantic_plugin`, then you can use it like this:
+
+```py test="skip"
+from pydantic import BaseModel
+
+class Foo(BaseModel, pydantic_plugin='all'):
+    ...
+```
+
+On each validation call, a callable registered for the event `all` will be called with the
+instance of `Foo`, the event name, and the validation result.

mkdocs.yml

@@ -111,6 +111,7 @@ nav:
   - 'datamodel-code-generator': integrations/datamodel_code_generator.md
   - 'devtools': integrations/devtools.md
   - 'Rich': integrations/rich.md
+  - 'Pydantic Plugins': integrations/plugins.md
 - Contribute: contributing.md
 - Blog:
   - blog/pydantic-v2-final.md

pydantic/plugin/loader.py

@@ -2,8 +2,10 @@
 
 Plugins are installed via Python entry points, for example in `pyproject.toml`:
 
-    [project.entry-points.pydantic]
-    pydantic_sdk = "pydantic_sdk:main"
+```toml
+[project.entry-points.pydantic]
+pydantic_sdk = "pydantic_sdk:main"
+```
 
 The entry point group is `pydantic` and the name of the entry point is the name of the plugin.