diff --git a/manual/plugins.rst b/manual/plugins.rst
index f609589c70..f430ebf791 100644
--- a/manual/plugins.rst
+++ b/manual/plugins.rst
@@ -196,12 +196,4 @@ Viewer plugins
    :members:
    :member-order: bysource
 
-Edit Book plugins
---------------------
-
-.. autoclass:: calibre.gui2.tweak_book.plugin.Tool
-   :show-inheritance:
-   :members:
-   :member-order: bysource
-
 
diff --git a/manual/polish.rst b/manual/polish.rst
index 43f10dc85b..9537ceabda 100644
--- a/manual/polish.rst
+++ b/manual/polish.rst
@@ -121,6 +121,15 @@ Working with the Table of Contents
 .. autofunction:: create_inline_toc
 
 
+Edit Book Tool
+--------------------
+
+.. autoclass:: calibre.gui2.tweak_book.plugin.Tool
+   :show-inheritance:
+   :members:
+   :member-order: bysource
+
+
 Controlling the editor's user interface
 -----------------------------------------
 
diff --git a/src/calibre/customize/__init__.py b/src/calibre/customize/__init__.py
index 38f61d49ff..7569dc107e 100644
--- a/src/calibre/customize/__init__.py
+++ b/src/calibre/customize/__init__.py
@@ -39,6 +39,8 @@ class Plugin(object):  # {{{
     Useful methods:
 
         * :meth:`temporary_file`
+        * :meth:`__enter__`
+        * :meth:`load_resources`
 
     '''
     #: List of platforms this plugin works on
@@ -263,6 +265,12 @@ class Plugin(object):  # {{{
             return False
 
     def __enter__(self, *args):
+        '''
+        Add this plugin to the python path so that it's contents become directly importable.
+        Useful when bundling large python libraries into the plugin. Use it like this::
+            with plugin:
+                import something
+        '''
         if self.plugin_path is not None:
             from calibre.utils.zipfile import ZipFile
             zf = ZipFile(self.plugin_path)
@@ -272,6 +280,7 @@ class Plugin(object):  # {{{
             for ext in ('pyd', 'so', 'dll', 'dylib'):
                 if ext in extensions:
                     zip_safe = False
+                    break
             if zip_safe:
                 sys.path.insert(0, self.plugin_path)
                 self.sys_insertion_path = self.plugin_path
diff --git a/src/calibre/gui2/tweak_book/plugin.py b/src/calibre/gui2/tweak_book/plugin.py
index af77d58a58..1c4bf4675d 100644
--- a/src/calibre/gui2/tweak_book/plugin.py
+++ b/src/calibre/gui2/tweak_book/plugin.py
@@ -17,6 +17,22 @@ from calibre.gui2.tweak_book.boss import get_boss
 
 class Tool(object):
 
+    '''
+    .. module:: calibre.gui2.tweak_book.plugin.Tool
+
+    The base class for individual tools in an Edit Book plugin. Useful members include:
+
+        * ``self.plugin``: A reference to the :class:`calibre.customize.Plugin` object to which this tool belongs.
+        * self. :attr:`boss`
+        * self. :attr:`gui`
+
+    Methods that must be overridden in sub classes:
+
+        * :meth:`create_action`
+        * :meth:`register_shortcut`
+
+    '''
+
     #: Set this to a unique name it will be used as a key
     name = None
 
@@ -103,7 +119,9 @@ def load_plugin_tools(plugin):
     else:
         for x in vars(main).itervalues():
             if isinstance(x, type) and x is not Tool and issubclass(x, Tool):
-                yield x()
+                ans = x()
+                ans.plugin = plugin
+                yield ans
 
 def plugin_action_sid(plugin, tool, for_toolbar=True):
     return plugin.name + tool.name + ('toolbar' if for_toolbar else 'menu')