different syntax

gistfile1.txt

This is from the DevOps Projects course:
https://www.udemy.com/course/devopsprojects/learn/lecture/33799740#notes

stage('Build App Image') {
            steps {
                script {
                    dockerImage = docker.build(appRegistry + ":$BUILD_NUMBER", "./Docker-files/app/multistage/")
                }
            }
        }
        
 This is from 
 https://docs.cloudbees.com/docs/admin-resources/latest/plugins/docker-workflow#docker-workflow-sect-build
 
 node {
  git '…' // checks out Dockerfile and some project sources
  def newApp = docker.build "mycorp/myapp:${env.BUILD_TAG}"
  newApp.push()
}

The different syntax in the documentation confuses me.