The color 255 is transparent. The screens may not be inorder and should be referenced by their file offset. Also the file may have extra space that is unused. This is so that map editors can change screens in the middle of the file without moving all the screens to fill all available space. Many more commands are planned.
Commands are variable length.
The first byte identifies the function and is followed by a variable number of arguments. Filenames have a maximum of 8 characters plus the extension. For example the key saves the current number of keys. There is nothing that lists the size of this data or what it contains. The current world definition file is a simple text file.