Some tag names produce errors

This is not an urgent issue, just extremely annoying for new users.

Some tag names can be whatever you want but other must be defined with specific formats because they are hard-coded into prepost/dlcdefs.py. At some point we need to :

1. Come up with a unified tag system. (Capitals? Spaces? Names for common variables?)
2. Document all tags

assigned to @dave

closed

lets track this under issue #37