Dave Matthews says he used to use "" or " " for ?Text where he wanted
to skip an item in a multiple-item field, as in
> Probe : "xyz"
> Wheat_polymorphism "" HindIII "0.0 (1,13)"
We made this illegal in 4_5. This was necessary because all items in
a class must have a unique name, and the 0th item with an implicit
empty name was already used for storing the model. (Remember that
?Text is a handled as a class just like ?Probe). It turns out that
using "" gave spurious references to the models, and even allowed
people to edit the models in alarming ways. This was definitely a
bug/loophole.
I suggest that you use some symbol such as "-" as a convention for
missing data.
You can still have empty Text, as opposed to ?Text.
Richard
