#3 Constrained attribute values in Browser

[Neil Earnshaw]

The Browser presents an Attribute table that allows users to
define the attributes of a model object. At the moment, the
values a simple text strings.

PB should support constraints on the values that can be
entered, preferably through the use of pull-down menus and
other user-friendly controls.

Some attributes take a single value, such as association
cardinalities (1..1, 1..*, etc.). Others, like archetypes(tags)
can take a list of values that need to be configurable, as
different code generators may support different sets of
archetypes.

At the moment, browsable objects are given the opportunity
to add a menu to the attribute table cells, but none of the
browsables are taking advantage of this.