Example 1

template.yml

#@ load("@ytt:template", "template")

#! First, capture the YAML document in a "Fragment Function"
#!
#@ def my_template(foo):
---
field1: #@ foo + "1"
field2: #@ foo + "2"
#@ end

#@ def another_template(prefix):
#@   return my_template(prefix + "-yada-")
#@ end

#! Again, in the same file, I start a YAML document (`---`), and replace it with the document produced by `another_template()`, passing in the value for `foo`:
--- #@ template.replace(another_template("a"))
--- #@ template.replace(another_template("b"))