Partial custom fields design document

[Gervase Markham]

Daniel Berlin wrote:
> Again, either way could be changed to the other later on if it is found 
> to be a large problem. I don't see why this is a "central issue" that 
> must be decided right now.

Because an ounce of prevention is worth a pound of cure. A design 
document is far easier to change than 50 working Bugzillas.

If we can't see any difference between the approaches, or if we can't 
know which is best until we try it, then sure, let's implement one and 
see. But I don't think that's the case - at least not yet.

Gerv