Document resuing styles.

doc/sources/guide/lang.rst

@@ -334,6 +334,58 @@ template instead, like so:
 `ctx` is a keyword inside a template that can be used to access the individual
 attributes of each instance of this template.
 
+Re-using styles in multiple widgets
+------------------------------------------------------------
+
+Consider the code below in my.kv:
+
+.. code-block:: kv
+
+    <MyFirstWidget>:
+        Button:
+            on_press: self.text(txt_inpt.text)
+        TextInput:
+            id: txt_inpt
+
+    <MySecondWidget>:
+        Button:
+            on_press: self.text(txt_inpt.text)
+        TextInput:
+            id: txt_inpt
+
+In myapp.py:
+
+.. code-block:: py
+
+    ...
+    class MyFirstWidget(BoxLayout):
+
+        def text(self, val):
+            print 'text input text is: {txt}'.format(txt=val)
+
+    class MySecondWidget(BoxLayout):
+
+        writing = StringProperty('')
+
+        def text(self, val):
+            self.writing = val
+    ...
+
+Because both classes share the same .kv style, this design can be simplified
+if we reuse the style for both widgets. You can do this in .kv as follows.
+In my.kv:
+
+.. code-block:: kv
+
+    <-MyFirstWidget,-MySecondWidget>:
+        Button:
+            on_press: self.text(txt_inpt.text)
+        TextInput:
+            id: txt_inpt
+
+By appending a dash before each class name, all the classes listed in the
+declaration will have the same kv properties.
+
 Designing with the Kivy Language
 --------------------------------