GetLabels parses the Dockerfile in the provided Reader and returns all discovered labels as provided by the LABEL instruction, with variables resolved and expanded.

NewUnquote returns an Unquote ready to use with the escape metacharacter set to '\'.

NewVars returns a Vars with the metacharacter set to '\' and no variables defined.

VarMeta is the metacharacter for variables.

Unquote is a text transformer that undoes one level of quoting.

Vars is a text transformer that does variable expansion as described in the Dockerfile Reference document.