MOFM2T11 — Section: 7.3, 8.1, 8.1.17

MTL defines an "open mode" to define how file blocks should behave : whether they append to existing files or overwrite them is defined this way. These two modes are not sufficient : users might want to generate files only when they don't exist. This can be either the very first transformation they execute (thus the file doesn't exist and need be created) or a latter generation when the user has deleted (inadvertently or on purpose) the target file. This is useful for configuration files that do not accept comments (thus rendering protected blocks unusable as these need a marker). An example of such a file is java's MANIFEST.MF file which format is extremely rigid.