+return value. The values of variables persists across calls to the
+same hook, but is NOT available to other hooks. To make the value of a
+variable available to other hooks, use the get and set methods. Each
+hook description lists the variables and return value expected, if
+any.
+
+The following special functions are available to hooks:
+* say msg
+ Displays the string msg to the user at the bottom of the screen.
+* log msg
+ Adds the string msg to the log, which the user can access via the
+ buffer list.
+* ask_yes_or_no question
+ Prompts the user with the string question for a yes or no
+ response. Returns true if the user answered yes, false otherwise.
+* get key
+ Gets the cross-hook value associated with key (which is typically a
+ string). If there is no value for a given key, nil is returned.
+* set key value
+ Sets the cross-hook value associated with key to value. key is
+ typically a string, while value can be whatever type it needs to be,
+ including nil.