Of course, it doesn't really matter for the simulator how you specify memory contents, so long as the results are correct. This must be the first character of the line. The various items should be separated by white space. The first line of a file is recognized as an instruction unless otherwise noted. If the mode is not specified, the previous mode is used.
Unlabelled items go in the next address.
There may be blank lines between lines of data. The first line of each file must contain a label so the simulator knows where to load the data. After that, line labels are optional. The end of a file is marked by EOF at the bottom of the file. The EOF must be on a line by itself.