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docs/extensions/extensions.md

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+# WinSW extensions
+
+Starting from WinSW 2.0, the wrapper provides an internal extension engine and several extensions.
+These extensions allow to alter the behavior of the Windows service in order to setup the required service environment.
+
+## Available extensions
+
+* [Shared Directory Mapper](shared-directory-mapper.md) - Allows mapping shared drives before starting the executable
+* [Runaway Process Killer](runaway-process-killer.md) - Termination of processes started by the previous runs of WinSW
+
+## Developer guide
+
+In WinSW v2 the extension does not support inclusion of external extension DLLs.
+
+### Adding external extensions
+
+The only way to create an external extension is to create a new extension DLL and 
+  then to merge this DLL into the executable using tools like `ILMerge`.
+See the example in `src/Core/ServiceWrapper/winsw.csproj`.
+
+Generic extension creation guideline:
+* Extension DLL should reference the `WinSWCore` library.
+* The extension should extend the `AbstractWinSWExtension` class.
+* The extension then can override event handlers offered by the upper class.
+* The extension should implement the configuration parsing from the `XmlNode`.
+* The extension should support disabling from the configuration file.
+
+WinSW engine will automatically locate your extension using the class name in the [XML configuration file](../xml-config-file.md).
+See configuration samples provided for the extensions in the core.
+For extensions from external DLLs, the `className` field should also specify the assembly name. 
+It can be done via fully qualified class name or just by the `${CLASS_NAME}, ${ASSEMBLY_NAME}` declaration.
+
+Please note that in the current versions of WinSW v2 the binary compatibility of extension APIs **is not guaranteed**.