Whats the meaning of "with" in gradle

In the answer https://stackoverflow.com/a/35879150 there is a with in the last line:

task gen (type: Jar) {
    description "Generates JAR without version number."
    archiveName = filename + ".jar"
    manifest {attributes 'Main-Class': mainFile}
    with jar
}

What is the exact meaning, and where is it documented? I couldn't find it in the gradle documentation and the with in groovy (http://groovy-lang.org/style-guide.html#_using_with_for_repeated_operations_on_the_same_bean) seems to be different.