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+An extension is just a subdirectory in the `extensions` directory.
+
+Web ui interacts with installed extensions in the following way:
+
+- extension's scripts in the `scripts` directory are executed as if they were just usual user scripts, except:
+  - `sys.path` is extended to include the extension directory, so you can import anything in it without worrying
+  - you can use `scripts.basedir()` to get the current extension's directory (since user can name it anything he wants)
+- extension's javascript files in the `javascript` directory are added to the page
+- extension's `style.css` file is added to the page
+