Adding Content Info on Binding and JS Variable

This bug to track content addition wrt Binding and JS Variable.

As suggested by Siri, content to ensure all 3 problems that Eben has run into are clearly documented:

• Where log(...) messages go. We may have to highlight this in a callout.
• The fact that buckets need bindings to be usable in handlers.
• The fact that JS exceptions are discarded unless try...catch is there to handle it.