** Program location
Defaults to $801 for ROM-based Applesoft. Locations $67/$68 point to
the start of the program, and the byte preceding it must be #0.

Details:
- http://www.atarimagazines.com/compute/issue11/36_1_THE_APPLE_GAZETTE_RESOLVING_APPLESOFT_AND_HIRES_GRAPHICS_MEMORY_CONFLICTS.php
- http://retrocomputing.stackexchange.com/questions/1604

** Format
DOS stores an additional byte on the end, which should be ignored.
** Parsing
See PARSE.INPUT.LINE at
http://www.txbobsc.com/scsc/scdocumentor/D52C.html

"AT" is ambiguous: it could also be "ATN" or "A TO". Applesoft checks
by seeing if the character directly after "AT" is "N" OR "O", and
forcing a non-match with "AT" if so. Note that this doesn't skip
blanks.

Data statements and REM statements seem to leave characters completely
intact (including storing the space, if any, after the "REM" or "DATA"
keyword).