Steps to reproduce the issue

• Install attached test plugin plg_test.zip
• go to Test plugin configuration, there is subform field called Test
• add 2 elements to this field
• it contains another subform field, ad some elements to it also
• drag the outer form element
• drag the inner form element

Expected result

Outer elements could not be dropped inside inner form, inner elements could not be dropped outside its scope.

Actual result

All elements (inner and outer) could be dropped anywhere

System information (as much as possible)

Joomla 4.0.6

Additional comments

Fields definition contains nested subform:

        <field name="test_outer" class="test1" type="subform" layout="joomla.form.field.subform.repeatable" multiple="true" label="Test outter" hiddenLabel="true">
          <form>
            <field name="test_inner" class="test2" type="subform" layout="joomla.form.field.subform.repeatable" hiddenLabel="true" multiple="true" label="Test Inner">
              <form>
                <field name="test_value" type="text" label="Test value" />
              </form>
            </field>
          </form>
        </field>

In joomla-field-subform.js file seems to be prepared some solution for this. It requires set rows-container attribute, which is not used in joomla.form.field.subform.repeatable. I tried to add there rows-container="joomla-field-subform" and seems it solved dragging outer elements inside the inner form. But not dragging inner elements to outer form.