What is proofOfWorkLimit?
The first byte, 1D, is the length. The next three bytes are the high bytes of the hash. So we have 00ffff, then we add ff bytes onto the end to get to 29 bytes. Then we're done.

We wind up with 3 bytes of leading zeroes because 32-29 is 3. And we get one byte of zeroes from the second byte of the compact bits. So the final result is 00,00,00,00,ff,ff,ff...