explain nrsign & lsign?

[snowcrash+gnupg-users]

hi,

i've a 'master', high-strength signing key, "A".

i'm using it to tsign another key, "B".

i note i can also nrsign(non-revocable)/lsign(non-exportable) "B" with "A".

can someone please clearly explain the consequences of doing so?

e.g., if i lsign "B" with "A", *which* key, then is made
non-exportable?  "A" or "B"?

i've googled for clarity, but other than the man page -- which doesn't
go into much depth -- have yet to find cases/examples.

thanks!