Index: /applications/editors/josm/plugins/comfort0/build.xml
===================================================================
--- /applications/editors/josm/plugins/comfort0/build.xml	(revision 35292)
+++ /applications/editors/josm/plugins/comfort0/build.xml	(revision 35293)
@@ -7,5 +7,5 @@
 
     <property name="plugin.author" value="simon04"/>
-    <property name="plugin.class" value="org.wikipedia.WikipediaPlugin"/> <!--TODO-->
+    <property name="plugin.class" value="net.simon04.comfort0.Comfort0Plugin"/>
     <property name="plugin.description" value="Allows editing data in Level0L format"/>
     <property name="plugin.icon" value="images/thetha.svg"/>
Index: /applications/editors/josm/plugins/comfort0/src/net/simon04/comfort0/Comfort0Plugin.java
===================================================================
--- /applications/editors/josm/plugins/comfort0/src/net/simon04/comfort0/Comfort0Plugin.java	(revision 35293)
+++ /applications/editors/josm/plugins/comfort0/src/net/simon04/comfort0/Comfort0Plugin.java	(revision 35293)
@@ -0,0 +1,26 @@
+package net.simon04.comfort0;
+
+import org.openstreetmap.josm.gui.MainApplication;
+import org.openstreetmap.josm.gui.MainMenu;
+import org.openstreetmap.josm.plugins.Plugin;
+import org.openstreetmap.josm.plugins.PluginInformation;
+
+/**
+ * Main class for the comfort0 plugin.
+ *
+ * @author Simon Legner <Simon.Legner@gmail.com>
+ */
+public class Comfort0Plugin extends Plugin {
+
+    /**
+     * Constructs a new {@link Comfort0Plugin}.
+     *
+     * @param info the plugin information describing the plugin.
+     */
+    public Comfort0Plugin(PluginInformation info) {
+        super(info);
+        final MainMenu menu = MainApplication.getMenu();
+        MainMenu.add(menu.editMenu, new EditLevel0LAction());
+
+    }
+}
Index: /applications/editors/josm/plugins/comfort0/src/net/simon04/comfort0/EditLevel0LAction.java
===================================================================
--- /applications/editors/josm/plugins/comfort0/src/net/simon04/comfort0/EditLevel0LAction.java	(revision 35293)
+++ /applications/editors/josm/plugins/comfort0/src/net/simon04/comfort0/EditLevel0LAction.java	(revision 35293)
@@ -0,0 +1,127 @@
+package net.simon04.comfort0;
+
+import static org.openstreetmap.josm.tools.I18n.tr;
+
+import java.awt.event.ActionEvent;
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.nio.charset.Charset;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+import java.util.Objects;
+
+import net.simon04.comfort0.level0l.parsergen.Level0LParser;
+import net.simon04.comfort0.level0l.parsergen.ParseException;
+import org.openstreetmap.josm.actions.JosmAction;
+import org.openstreetmap.josm.command.ChangePropertyCommand;
+import org.openstreetmap.josm.command.Command;
+import org.openstreetmap.josm.command.SequenceCommand;
+import org.openstreetmap.josm.data.UndoRedoHandler;
+import org.openstreetmap.josm.data.osm.DataSet;
+import org.openstreetmap.josm.data.osm.OsmPrimitive;
+import org.openstreetmap.josm.data.osm.PrimitiveData;
+import org.openstreetmap.josm.data.osm.RelationData;
+import org.openstreetmap.josm.data.osm.WayData;
+import org.openstreetmap.josm.gui.MainApplication;
+import org.openstreetmap.josm.gui.util.GuiHelper;
+import org.openstreetmap.josm.tools.Logging;
+
+/**
+ * Edit the selected objects in an external editor in the Level0L format.
+ */
+public class EditLevel0LAction extends JosmAction {
+
+    private static final Charset CHARSET = Charset.defaultCharset();
+
+    /**
+     * Constructs a new {@link EditLevel0LAction}.
+     */
+    public EditLevel0LAction() {
+        super(tr("Edit as Level0L"),
+                "theta",
+                tr("Edit the selected objects in an external editor in the Level0L format"),
+                null, false);
+    }
+
+    @Override
+    public void actionPerformed(ActionEvent e) {
+        try {
+            editLevel0();
+        } catch (Exception ex) {
+            ex.printStackTrace();
+        }
+    }
+
+    private void editLevel0() throws IOException {
+        final DataSet dataSet = MainApplication.getLayerManager().getEditDataSet();
+        final Path path = writeLevel0(dataSet);
+        final Process editor = new ProcessBuilder("kate", path.toString()).start();
+        Logging.info("Comfort0: Launching editor on file {0}", path);
+        new Thread(() -> awaitEditing(dataSet, path, editor), path.getFileName().toString()).start();
+    }
+
+    private Path writeLevel0(DataSet dataSet) throws IOException {
+        final byte[] level0 = new OsmToLevel0L().visit(dataSet.getSelected())
+                .toString()
+                .replace("\u200E", "")
+                .replace("\u200F", "")
+                .getBytes(CHARSET);
+        final Path path = Files.createTempFile("level0", ".txt");
+        Files.write(path, level0);
+        return path;
+    }
+
+    private void awaitEditing(DataSet dataSet, Path path, Process editor) {
+        try {
+            editor.waitFor();
+            Logging.info("Comfort0: Editing of file {0} done", path);
+            readLevel0(path, dataSet);
+            Files.delete(path);
+        } catch (Exception ex) {
+            ex.printStackTrace();
+        }
+    }
+
+    private void readLevel0(Path path, final DataSet dataSet) throws IOException, ParseException {
+        final List<PrimitiveData> primitives;
+        try (BufferedReader reader = Files.newBufferedReader(path, CHARSET)) {
+            primitives = new Level0LParser(reader).primitives();
+        }
+        Logging.info("Comfort0: Reading file {0} yielded {1} primitives", path, primitives.size());
+
+        buildChangeCommands(dataSet, primitives);
+    }
+
+    private void buildChangeCommands(DataSet dataSet, List<PrimitiveData> primitives) {
+        final List<Command> commands = new ArrayList<>();
+        for (PrimitiveData fromLevel0L : primitives) {
+            final OsmPrimitive fromDataSet = dataSet.getPrimitiveById(fromLevel0L);
+
+            // TODO handle way nodes, relation members
+            if (fromLevel0L instanceof WayData) {
+                ((WayData) fromLevel0L).setNodeIds(Collections.emptyList());
+            } else if (fromLevel0L instanceof RelationData) {
+                ((RelationData) fromLevel0L).setMembers(Collections.emptyList());
+            }
+
+            final OsmPrimitive newInstance = fromLevel0L.getType().newVersionedInstance(fromDataSet.getUniqueId(), fromDataSet.getVersion());
+            newInstance.load(fromLevel0L);
+
+            final boolean equalKeys = Objects.equals(newInstance.getKeys(), fromDataSet.getKeys());
+            if (!equalKeys) {
+                final ChangePropertyCommand command = new ChangePropertyCommand(Collections.singleton(fromDataSet), newInstance.getKeys());
+                commands.add(command);
+            }
+        }
+
+        Logging.info("Comfort0: Changing {0} primitives", commands.size());
+        if (commands.isEmpty()) {
+            return;
+        }
+        final SequenceCommand command = new SequenceCommand("Comfort0", commands);
+        GuiHelper.runInEDT(() -> UndoRedoHandler.getInstance().add(command));
+    }
+}