Is there a fundamental difference to template systems such as erb? Because I'm having a hard time seeing it (except the academic prose and the subtle horror xml always causes me).
It's a language powerful enough to let you design a custom template system, i.e. it's second-order meta-programming, pushing the leveraging potential way farther than most people would even consider offhand. This kind of thing doesn't matter so much when you have a system already described within a few thousand lines, but it gains credence as more of the code consists of business logic and data models - stuff that has its own programming ruleset.
An internal, interpreted DSL can be written to do similar, but I think the point of this tool is to ease the process of writing the DSL itself, and to make the resulting runtime efficient.
