feat: Implement 'lineSlider' point method and warn about 'align'

src/adapptlet.civet

@@ -196,6 +196,12 @@ function dispatchJcommand(
             Text("${value}", TitlePoint + (2,5))`
       'pivot'
          return  // already handled in postApplets
+      'align'
+         console.warn
+            'Label alignment is not available in GeoGebra'
+            'translation, as there is no facility for automatically'
+            'positioning labels. However, they can be dragged manually.'
+         return
       /e\[\d+\]/
          num := parseInt(name.slice(2))
          {commands, callbacks, parts} :=
@@ -592,6 +598,13 @@ classHandler: Record<JoyceClass, ClassHandler> :=
             if args.scalar and args.scalar.length
                callbacks.push (api: AppletObject) =>
                   api.setCoords name, ...args.scalar as XYZ
+         'lineSlider'
+            pt := args.subpoints
+            unless pt and pt.length is 2 then return
+            commands.push `${name} = Point(Line(${pt[0]}, ${pt[1]}))`
+            if args.scalar and args.scalar.length
+               callbacks.push (api: AppletObject) =>
+                  api.setCoords name, ...args.scalar as XYZ
          'midpoint'
             if args.line
                commands.push `${name} = Midpoint(${args.line[0]})`