Ah, of course... although this feature possibly raises the question of whether ddoc parsing should depend on -D.

-D says to output documentation, which isn't necessarily desired, and shouldn't really be a requirements for this feature.

Once we have access to ddoc from code and code may depend on this __traits, I wonder if the compiler should always parse out the ddoc blocks, even if they're not used otherwise (ie, if -D is not supplied).