$ perl -Mre=debug -wle 'm/C$\n^D/'
Freeing REx: `","'
Omitting $` $& $' support.

EXECUTING...

Compiling REx `C
n^D'
size 6 Got 52 bytes for offset annotations.
first at 1
rarest char D at 3
   1: EXACT <C\nn>(3)
   3: BOL(4)
   4: EXACT <D>(6)
   6: END(0)
anchored "C
...