Typos / rephrasing for clarity

theano/compile/mode.py

@@ -105,20 +105,20 @@ def register_OutputGuard_c_code(type):
 
 class OutputGuard(gof.Op):
     """
-    This op is used only internaly by Theano.
+    This op is used only internally by Theano.
 
     Only the AddDestroyHandler optimizer tries to insert them in the graph.
 
-    This Op is declared as destructive while is not destroying
+    This Op is declared as destructive while it is not destroying
     anything. It returns a view. This is used to prevent destruction of
-    the output variable of a Theano function.
+    the output variables of a Theano function.
 
-    There is mechanism in Theano that should prevent this, but the use
-    of OutputGuard add a safe guard. Maybe it is currently possible
-    that optimization run before the add_destroy_handler phase that
-    make some inplace optimization bypass this mechanism?
+    There is a mechanism in Theano that should prevent this, but the use
+    of OutputGuard adds a safeguard: it may be possible for some optimization
+    run before the add_destroy_handler phase to bypass this mechanism, by
+    making in-place optimizations.
 
-    TODO: find a current full explaination.
+    TODO: find a current full explanation.
     """
     destroy_map = {0:[0]}
     view_map = {0:[0]}