Dependency configuration userguide is missing important information

I came accross this example in the Gradle Userguide
It shows that I need to access configurations.preCompileJsps.asPath from within a doLast.
Sadly it does not explain how preCompileJsps is called.
I find no dependency declarations to preCompileJsps in the example.

Please explain how preCompileJsps is called during the build.

task preCompileJsps {
    doLast {