extension_plugin.xml

<extension point="com.luxoft.eclipse.fit.runner.fitSourceEditor">
	<sourceeditor class="org.eclipse.wst.sse.ui.StructuredTextEditor" id="com.luxoft.eclipse.fit.runner.optional.wtpHTMLEditor">
	</sourceeditor>
</extension>

plugin.xml

<element name="extension">
	<complextype>
		<sequence>
			<element ref="sourceEditor"></element>
		</sequence>
		...
	</complextype>
</element>

<element name="sourceEditor">
	<complextype>
		<attribute name="id" type="string" use="required">
			...
		</attribute>
		<attribute name="class" type="string" use="required">
			<annotation>
				<appinfo>
					<meta.attribute kind="java" basedon=":org.eclipse.ui.texteditor.ITextEditor">
				</meta.attribute>
			</appinfo>
		</annotation>
	</attribute>
</complextype>
</element>

SourceEditorFactory.java

public class SourceEditorFactory {
	private static IConfigurationElement cachedConfigurationElement;

	private static final String ATTRIBUTE_CLASS = "class";

	public static ITextEditor createSourceEditor() {
		if (cachedConfigurationElement == null) {
			cachedConfigurationElement = readConfigurationElement();
		}

		if (cachedConfigurationElement != null) {
			try {
				return (ITextEditor) cachedConfigurationElement
						.createExecutableExtension(ATTRIBUTE_CLASS);
			} catch (Exception exception) {
				// errors when initializing the source editor
			}
		}

		return new TextEditor();
	}

	// Reads the first configuration element whose implemented class is not
	// TextEditor
	private static IConfigurationElement readConfigurationElement() {
		IExtensionPoint extensionPoint = Platform.getExtensionRegistry()
				.getExtensionPoint(FitPlugin.PLUGIN_ID, "fitSourceEditor");

		for (IConfigurationElement configurationElement : extensionPoint
				.getConfigurationElements()) {
			if (!StringUtils.equals(TextEditor.class.getCanonicalName(),
					configurationElement.getAttribute(ATTRIBUTE_CLASS))) {
				return configurationElement;
			}
		}

		return null;
	}
}