823: Highlights

Value holders have a single instance variable, value, which is accessed via value and value: methods.
Value holders frequently connect controllers to viewers. Both the viewers and the controllers associated with a particular value holder access that value holder by sending a model message to self.
If you want to create a value holder, then instantiate the following pattern:
```
ValueHolder new 
```
Aspect adapters translate value and value: messages sent from viewers and controllers into model-specific getters and setters.
If you want to create an aspect adapter, then you must specify the receiver instance (the subject), along with an indication that update: messages are to be forwarded, and the name for the getter and setter accessors, by instantiating one of the following patterns. Note that the names are provided as #-marked literals, with no colons:
```
(AspectAdaptor new) subject: F; 
        subjectSendsUpdates: true; 
                  forAspect: accessor name 
(AspectAdaptor new) subject: F; 
        subjectSendsUpdates: true; 
                 accessWith: getter name  
                 assignWith: setter name} 
```