Template model. No template engine was installed. Results are the model's arithmetic.

Trusted source, no user text in the source:
  source: Sum: {{ 2 + 3 }}
  model result: Sum: 5

User text kept as data:
  source: Hello, {{ name }}
  name: 2 + 3
  model result: Hello, 2 + 3

User text compiled as the source:
  source: the caller's text
  The caller's text becomes the template.
  That is the boundary this lesson marks.