Q:

Gradle-Android: Where is the classpath() coming from?

Here is the root build.gradle file of an android app. I want to ask where does the classpath() method is declared. I guess in Project but I cant find it in the reference.
buildscript {

    repositories {
        google()
        jcenter()
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:3.0.1'

        // NOTE: Do not place your application dependencies here; they belong
        // in the individual module build.gradle files
    }
}

allprojects {
    repositories {
        google()
        jcenter()
    }
}

task clean(type: Delete) {
    delete rootProject.buildDir
}

A:

From the Interface ScriptHandler, classpath is the configuration's value of public static final String CLASSPATH_CONFIGURATION "classpath".   
You can call it via buildscript.CLASSPATH_CONFIGURATION as buildscript returns a ScriptHandler.

