<extension point="org.eclipse.ui.activities">
      <activity id="com.myExample.plugin.email.activity.emailPerspective" name="Email Perspective">
         <enabledWhen>
            <or>
               <with variable="EMAIL.ADMIN">
                  <equals value="ENABLED"> </equals>
               </with>
               <with variable="EMAIL_DELETE_EMAIL_ADDRESS">
                  <equals value="ENABLED"> </equals>
               </with>
               <with variable="EMAIL_DELETE_TEMPLATE">
                  <equals value="ENABLED"> </equals>
               </with>
               <with variable="EMAIL_FIND_EMAIL_AUDIT">
                  <equals value="ENABLED"> </equals>
               </with>
               <with variable="EMAIL_SAVE_TEMPLATE">
                  <equals value="ENABLED"> </equals>
               </with>
               <with variable="EMAIL_SAVE_EMAIL_ADDRESS">
                  <equals value="ENABLED"> </equals>
               </with>
               <with variable="EMAIL_FIND_TEMPLATES">
                  <equals value="ENABLED"> </equals>
               </with>
               <with variable="EMAIL_FIND_EMAIL_ADDRESS">
                  <equals value="ENABLED"> </equals>
               </with>
               <with variable="EMAIL_DELETE_AUDIT">
                  <equals value="ENABLED"> </equals>
               </with>
            </or>
         </enabledWhen>
      </activity>
      <activityPatternBinding activityId="com.myExample.plugin.email.activity.emailPerspective" pattern="com.myExample.plugin.email/com.myExample.plugin.email.perspective">
      </activityPatternBinding>
   </extension>

         <enabledWhen>
            <and>
               <with variable="CSIRoles">
                  <iterate ifEmpty="false" operator="or">
                     <equals value="EMAIL_FIND_EMAIL_ADDRESS">
                     </equals>
                  </iterate>
               </with>
               <with variable="activeWorkbenchWindow.activePerspective">
                  <equals value="com.example.email.perspective">
                  </equals>
               </with>
            </and>
         </enabledWhen>

public class WithExpression extends CompositeExpression {

	private String fVariable;
	private static final String ATT_VARIABLE= "variable";  //$NON-NLS-1$
	
	/**  the boolean flag indicating if you should return false or throw exception when a variable is null  */
	private boolean nullReturnsFalse = false;

	/**
	 * The seed for the hash code for all with expressions.
	 */
	private static final int HASH_INITIAL= WithExpression.class.getName().hashCode();

	public WithExpression(IConfigurationElement configElement) throws CoreException {
		fVariable= configElement.getAttribute(ATT_VARIABLE);
		Expressions.checkAttribute(ATT_VARIABLE, fVariable);
		
		String nullFalse = configElement.getAttribute("nullReturnsFalse"); //$NON-NLS-1$
		
		if(nullFalse != null)
			this.nullReturnsFalse = Boolean.parseBoolean(nullFalse);
	}
				.
				.
				.
				.
	public EvaluationResult evaluate(IEvaluationContext context) throws CoreException {
		Object variable= context.getVariable(fVariable);
		if (variable == null) {
			if(this.nullReturnsFalse)
				return EvaluationResult.FALSE;
			else
				throw new CoreException(new ExpressionStatus(
						ExpressionStatus.VARIABLE_NOT_DEFINED,
						Messages.format(ExpressionMessages.WithExpression_variable_not_defined, fVariable)));
		}
		if (variable == IEvaluationContext.UNDEFINED_VARIABLE) {
			return EvaluationResult.FALSE;
		}
		return evaluateAnd(new EvaluationContext(context, variable));
	}