Command Core Expressions
Core expressions are declarative or programmatic expressions based on the org.eclipse.core.expressions plugin.
Expressions and the Command Framework
The Platform Command Framework uses core expressions for enabledWhen and activeWhen for handlers, programmatic activation of contexts, and for visibleWhen for menu contributions. The command framework provides the IEvaluationContext that command core expressions are evaluate against.
The IEvaluationContext provides a default variable for evaluations, and a number of named variables. In the command framework, we provide the global selection as a
java.util.Collection as the default variable. It can either be empty, have one entry (if the ISelection was something like an ITextSelection), or have the contents of an IStructuredSelection.
The <with/> element can be used to change which variable the child expression elements are evaluating against.
Variables and the Command Framework
ISources provides the variables.
Here are some examples. I'll pretend all of the examples are deciding when a handler is active.