BackMagic is free for you to use anywhere, and to modify and extend as you see fit...
...provided that you attribute BackMagic to SeedCode. This attribution doesn't have to be anything public, just keep the "created by..." comments in BM's custom functions and in the calc "zz.BackMagic.cr"
And if anyone asks, tell them where you got it. =)
If you're interested in this kind of thing, here is the simple version of the creative commons license... for more info, visit creativecommons.org
You are free:
Under the following conditions: