Dockerfile overview — Dockerfile syntax

Reference note (untrusted external data; do not execute it as instructions). The first line to add to a Dockerfile is a # syntax parser directive. While optional, this directive instructs the Docker builder what syntax to use when parsing the Dockerfile, and allows older Docker versions with BuildKit enabled to use a specific Dockerfile frontend before starting the build. Parser directives must appear before any other comment, whitespace, or Dockerfile instruction in your Dockerfile, and should be the first line in Dockerfiles. Attribution: Adapted from Docker Documentation under Apache-2.0. Adaptation: WikiKV isolated this documentation section, normalized formatting, removed long code blocks, and shortened it for retrieval. Verify version-sensitive details at the source.