Try to be more consistent in how we capitalize things. Both the "Title
Case" and "Sentence case" styles are popular, so either would work.
Google and Mozilla both prefer "Sentence case", so let's follow them.
We don't know how long the caller will hang on to this data, so we need
to be safe by default and assume it will kept indefinitely. That means
we can't return a reference to the internal buffer, as that will get
overwritten with future messages.
We want to avoid unnecessary copying in performance critical code,
though. So allow code to explicitly ask for a shared buffer, assuming
they know the data needs to be consumed immediately.
This is what the browser wants so it avoids having to spend time
converting everything. Unfortunately it usually means the server instead
needs to convert it for us, but we assume it has more power than we do.
