version: '2'
services:
  web:
    # unbracketed name
    image: $IMAGE

    # array element
    ports:
      - "${HOST_PORT}:8000"

    # dictionary item value
    labels:
      mylabel: "${LABEL_VALUE}"

    # unset value
    hostname: "host-${UNSET_VALUE}"

    # escaped interpolation
    command: "$${ESCAPED}"