<p>Parameter extends Variable with additional support for string-valued
variables that makes these friendlier at the user interface level.
In particular, this class supports an annotation that specifies
choices for values. A user interface can use this to present a
choice dialog that offers the specified values. This is typically
used when a particular set of choices make sense. The values can
be any expression, or if used in conjunction with string mode,
any string.</p>
<p>
By default, an instance of Parameter, unlike Variable, is persistent.</p>
<p>
By convention, an instance of NamedObj has a set of attributes,
some of which are visible to users and some of which are not.
When a user interface presents these attributes
for editing, it presents only those that are visible.
By default, an instance of Parameter is visible, as indicated by the fact
that it returns FULL in its getVisibility() method. This can be overridden
by calling setVisibility().</p>
Neil Smyth, Edward A. Lee, Xiaojun Liu
$Id: Parameter.java 70398 2014-10-22 23:44:32Z cxh $
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