with with a single expression

[% with title='Hello World' fill site/header %] --EOF--
look inside...
Thus Spake Andy:

We can remove the braces because the block contains only a single expression. This is key to the flexibility of TT3's language. Rather than defining similar (but subtly different) directives like INCLUDE and PROCESS we instead have smaller, simpler units like with and fill that can be plugged together to make more complex expressions.