add connection to container block

grammar.js

@@ -111,7 +111,7 @@ module.exports = grammar({
     _new_container_block_definition: ($) =>
       prec(
         PREC.CONTAINER,
-        choice($._eol, seq(choice($.shape, $.container), $._end))
+        choice($._eol, seq(choice($.shape, $.container, $.connection), $._end))
       ),
 
     // --------------------------------------------

src/grammar.json

@@ -428,6 +428,10 @@
                   {
                     "type": "SYMBOL",
                     "name": "container"
+                  },
+                  {
+                    "type": "SYMBOL",
+                    "name": "connection"
                   }
                 ]
               },

test/corpus/connection.txt

@@ -196,3 +196,29 @@ foo.biz.baz -> bar.baz.biz: Label
     (label)
   )
 )
+
+================================================================================
+Connection of shapes inside a block of container
+================================================================================
+foo.baz: {
+  foo -> biz: Label
+}
+
+--------------------------------------------------------------------------------
+
+(source_file
+  (container
+    (container_key) (dot)
+    (container
+      (container_key)
+      (block
+        (connection
+          (shape_key)
+          (arrow)
+          (shape_key)
+          (label)
+        )
+      )
+    )
+  )
+)