Parameter param = ModelFactory.eINSTANCE.createParameter();
 param.setName("workflowsummary");
 param.setValue("my data....");

 <imixs:taskConfig>
          <imixs:parameter xsi:type="imixs:Parameter" name="workflowsummary" value="my data...."/>
</imixs:taskConfig> 

 <imixs:taskConfig>
          <imixs:parameter xsi:type="imixs:Parameter" name="workflowsummary" >my data....
        </imixs:parameter> 
</imixs:taskConfig> 

 <eClassifiers xsi:type="ecore:EClass" name="Parameter">
    <eStructuralFeatures xsi:type="ecore:EAttribute" name="name" eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EString"/>
    <eStructuralFeatures xsi:type="ecore:EAttribute" name="value" upperBound="-1"
        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EString"/>
  </eClassifiers>

<bpmn2:extensionElements>
 <imixs:taskConfig>
  <imixs:parameter xsi:type="imixs:Parameter" name="txtMailSubject">
    <value>Hello world</value>
  </imixs:parameter>
  <imixs:parameter xsi:type="imixs:Parameter" name="txtMailBody">
    <value>Some long message...</value>
  </imixs:parameter>
  <imixs:parameter xsi:type="imixs:Parameter" name="txtMailReceifer">
    <value>test@a.com</value>
    <value>test@b.com</value>
  </imixs:parameter>
 </imixs:taskConfig>
</bpmn2:extensionElements>

	EList<String> valueList = subjectParam.getValue();

....
	Parameter subjectParam = getProperty("txtMailSubject");
	// this did not work because only the first element of the value list should be bound.....?
	bindAttribute(getAttributesParent(),subjectParam,"value", "Subject");					
...

public class MailPropertySection extends AbstractImixsPropertySection {

	final static EStructuralFeature METADATA_FEATURE = ModelPackage.eINSTANCE.getDocumentRoot_MetaData();
	final static EStructuralFeature METADATA_VALUE = ModelPackage.eINSTANCE.getMetaData_Value();

	@Override
	protected AbstractDetailComposite createSectionRoot() {
		return new MailDetailComposite(this);
	}

	@Override
	public AbstractDetailComposite createSectionRoot(Composite parent, int style) {
		return new MailDetailComposite(parent, style);
	}

	public class MailDetailComposite extends AbstractDetailComposite {
		public MailDetailComposite(AbstractBpmn2PropertySection section) {
			super(section);
		}

		public MailDetailComposite(Composite parent, int style) {
			super(parent, style);
		}

		@Override
		public void createBindings(final EObject be) {
			if (be==null || !(be instanceof IntermediateCatchEvent)) {
				return;
			}
			
			setTitle("Mail Configuration");
			
			 // create a new Property Tab section with a twistie
	        Composite section = createSectionComposite(this, "Mail Body");
	        // get the MetaData object from this BaseElement's extension elements
	        MetaData metaData = (MetaData) findExtensionAttributeValue((BaseElement)be, METADATA_FEATURE,"txtSubject");
	        if (metaData==null) {
	        	// create the new MetaData and insert it into the
                // BaseElement's extension elements container
                // Note that this has to be done inside a transaction
                TransactionalEditingDomain domain = getDiagramEditor().getEditingDomain();
                domain.getCommandStack().execute(new RecordingCommand(domain) {
                    @Override
                    protected void doExecute() {
                    	MetaData metaData = ModelFactory.eINSTANCE.createMetaData();
                        metaData.setValue("Some Subject....");
                        metaData.setName("txtSubject");
                        addExtensionAttributeValue((BaseElement)be, METADATA_FEATURE, metaData);
                        setBusinessObject(be);
                    }
                });
	        } else {
	        	 TextObjectEditor valueEditor = new TextObjectEditor(this, metaData, METADATA_VALUE);
	            // valueEditor.setMultiLine(true);
	            
	             valueEditor.createControl(this, "Value");
	        }
		}
		
		
		/**
		 * Add a new extension element to the given BaseElement.
		 */
		void addExtensionAttributeValue(BaseElement be, EStructuralFeature feature, Object value) {
			ExtensionAttributeValue eav = null;
			if (be.getExtensionValues().size()>0) {
				// reuse the <bpmn2:extensionElements> container if this BaseElement already has one
				eav = be.getExtensionValues().get(0);
			}
			else {
				// otherwise create a new one
				eav = Bpmn2Factory.eINSTANCE.createExtensionAttributeValue();
				be.getExtensionValues().add(eav);
			}
			eav.getValue().add(feature, value);
		}
		
		/**
		 * Find the first entry in this BaseElement's extension elements container
		 * that matches the given structural feature MetaData and the name.
		 */
		Object findExtensionAttributeValue(BaseElement be, EStructuralFeature feature,String itemName) {
		    for (ExtensionAttributeValue eav : be.getExtensionValues()) {
		        for (FeatureMap.Entry entry : eav.getValue()) {
		            if (entry.getEStructuralFeature() == feature) {		            	
		            	if (entry.getValue() instanceof MetaData) {
		            		MetaData confItem=(MetaData) entry.getValue();
		            		if (confItem.getName().equals(itemName))
		            			return confItem;
		            			//return entry.getValue();		            
		            	}
		            }
		        }
		    }
		    return null;
		}
	}
}

@Override
public void createBindings(final EObject be) {
	if (be == null || !(be instanceof IntermediateCatchEvent)) {
		return;
	}
	setTitle("Mail Configuration");
	// create a new Property Tab section with a twistie
	Composite section = createSectionComposite(this, "Mail Body");
	// get the MetaData object from this BaseElement's extension
	// elements
	ConfigItem metaData = (ConfigItem) findExtensionAttributeValue(
			(BaseElement) be, METADATA_FEATURE, "txtSubject");
	if (metaData == null) {
		// create the new MetaData and insert it into the
		// BaseElement's extension elements container
		metaData = ModelFactory.eINSTANCE.createConfigItem();
		metaData.setValue("Some Subject....");
		metaData.setName("txtSubject");
		// addExtensionAttributeValue
		ExtensionAttributeValue eav = null;
		if (((BaseElement) be).getExtensionValues().size() == 0) {
			// otherwise create a new one
			eav = Bpmn2Factory.eINSTANCE
					.createExtensionAttributeValue();
			InsertionAdapter.add(eav, METADATA_FEATURE, metaData);
			InsertionAdapter.add(be, Bpmn2Package.eINSTANCE
					.getBaseElement_ExtensionValues(), eav);
		} else {
			// reuse the <bpmn2:extensionElements> container if this
			// BaseElement already has one
			eav = ((BaseElement) be).getExtensionValues().get(0);
		}
	}
	TextObjectEditor valueEditor = new TextObjectEditor(this, metaData,
			METADATA_VALUE);
	// valueEditor.setMultiLine(true);
	valueEditor.setStyle(SWT.MULTI | SWT.V_SCROLL);
	valueEditor.createControl(this, "Value");
}