The Commodore Macro Assembler is an interesting beast, largely because the machine has no built-in text editor except for editing BASIC programs by line (cc @joe@f.duriansoftware.com. So, how do you enter assembler source on the C64? You load a little wedge which adds a couple of BASIC commands like auto and renumber (which the C64 doesn't already have), and it turns off line tokenization. And then they just reuse the BASIC editor. You just enter the assembler program with line numbers like BASIC, and because it isn't tokenized, the line just carries the plain text. You then save this with the regular SAVE command, which has been patched by the wedge to save the raw text without the line numbers and sequence pointers.