Problem:
Validation messages are not consistently formatted.
- Parameter names sometimes are NOT quoted.
- Descriptive names (non-parameters) sometimes ARE quoted.
Solution:
Always quote the `name` value passed to a VALIDATE macro _unless_ the
value has whitespace.
Before this, --embed UIs (without --headless) would not trigger UIEnter.
For TUI, maybe UIEnter isn't useful, but:
- It is less "surprising"/special.
- Makes documentation simpler.
- When TUI becomes a coprocess, it will happen anyway.
