What does ext.kotlin_version = '+' mean in Build.gradle?

Question

The following code is from https://github.com/android/camera/blob/master/CameraXBasic/build.gradle

What does ext.kotlin_version = '+' mean in Build.gradle?

Build.gradle

buildscript {
    // Top-level variables used for versioning
    ext.kotlin_version = '+'
    ext.java_version = JavaVersion.VERSION_1_8

    repositories {
        google()
        jcenter()
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:3.4.1'
        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
        classpath "androidx.navigation:navigation-safe-args-gradle-plugin:2.0.0"

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

Normal Code

buildscript {
    ext.kotlin_version = '1.3.41'
    ext.anko_version = '0.10.8'

    repositories {
        google()
        jcenter()

    }
    dependencies {
        classpath 'com.android.tools.build:gradle:3.4.1'
        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
        // NOTE: Do not place your application dependencies here; they belong
        // in the individual module build.gradle files
    }
}

Answer 1

Often times we see '+' as such:

compile 'com.android.support:appcompat-v7:23.0.+'

Which means version 23.0.0 or higher as long as it starts with 23.0.

In your case it means the latest version, could be 1.0.0, 2.1.0, 0.0.1, 25.10.100 or anything that is latest. But I would like to note out that this is bad practice as this could produce non-deterministic builds, meaning one time the source code could build successfully and another time it might fail without ever modifying anything in it. For more info check this link: https://blog.danlew.net/2015/09/09/dont-use-dynamic-versions-for-your-dependencies/