DefaultForm format is the default instruction line.

ExecForm format instruction arguments to an exec form, like ["/bin/bash"].

KeyValueForm format instruction arguments and add '=' between a key and a value, like `LABEL key=value`.

Marshal takes a dockerfile node as parameter, parse its AST graph then return line by line as a string Remark: Dockerfile Comments are not yet supported and therefor deleted in the process.

ShellForm format a line instruction containing shell commands, like RUN "echo true && echo false".