You would have to program your own interpreter. The //! import directive is normally used for .j files. It will either show errors or do nothing at all to the xml file.
Otherwise I recommend that you look into GMSI. It helps a lot for tedious creations. You can also use Lua but some people say it doesn't work on Windows 8, and it is a bit limited in some aspects compared to GMSI.
It depends on what you are trying to do. Are you trying to make objects or are you just trying to type JASS code?
Creating a custom compiler probably isn't the easier task. If you are making objects, then your compiler would have to translate your XML code to write the particular objects into the map's MPQ, similar to what GMSI/Lua does. Alternatively (better option IMO), you could write a parser to translate your XML code into GMSI code or Lua code. But of course, this means you have to have knowledge of the code you're translating to. So if it is just for personal use, then you might as well use the GMSI or Lua code.
You would have to program your own interpreter. The //! import directive is normally used for .j files. It will either show errors or do nothing at all to the xml file.
Otherwise I recommend that you look into GMSI. It helps a lot for tedious creations. You can also use Lua but some people say it doesn't work on Windows 8, and it is a bit limited in some aspects compared to GMSI.
Also, im quite familiar with accessing MPQs and reading XML code in a program, I just dont know the part about accessing the compiler.