Im not sure where this module/addon came from, but I used it with SS 2.4 and now with upgrading to SS 3.1 I am unable to get it to work.
I was hoping someone was able to take a look at it for me.

EditableCompositeField.php

<?php

class EditableCompositeField extends EditableFormField {

	static $singular_name = 'Container Field';
	
	static $plural_name = 'Containers';
	
	static $has_many = array(
		"SubFields" => "EditableFormField"
	);
	
	function getFormField() {
		$children = $this->SubFields();
		$field = new CompositeField();
		if($children && $children->exists()) {
			foreach($children as $child) {
				$field->push($child->getFormField());
			}
		}
		return $field;
	}
	public function IsContainer(){return true;}
}

There also seems to be some modifications within CSS

FieldEditor.css

		/** Container Fields **/
		
		#Fields_fields .EditableCompositeField ul.subFieldsList {
			min-height: 20px;
			padding-bottom: 10px;
			background: #f4f4f4;
			display: block;
			clear: both;
			margin-left: 38px;
		}
			#Fields_fields .EditableCompositeField ul.subFieldsList li {
				display: block;
				margin: 0 2px 0 7px;
				padding-left: 10px;
				background: white;
			}

and addition to EditableFormField.ss

	<% if IsContainer %>
		<ul class="subFieldsList ContainerField{$ID}">
			<% if SubFields %>
				<% control SubFields %>
					$EditSegment
				<% end_control %>
			<% end_if %>
		</ul>
	<% end_if %>

Is it possible to create a container field within SS3.1?
I seem to be missing something, adding these additions into the SS 3.1 userforms module and fixing depreciation didnt seem to work too well.
I was unable to drag onto the container field.

UPDATES:

EditableCompositeField:

<?php

class EditableCompositeField extends EditableFormField {

	private static $singular_name = 'Container Field';
	
	private static $plural_name = 'Containers';
	
	private static $has_many = array(
		"SubFields" => "EditableFormField"
	);
	
	public function getFormField() {
		$children = $this->SubFields();
		$field = new CompositeField();
		if($children && $children->exists()) {
			foreach($children as $child) {
				$field->push($child->getFormField());
			}
		}
		return $field;
	}
	public function IsContainer(){return true;}
}

   <% if IsContainer %>
      <ul class="subFieldsList ContainerField{$ID}">
         <% if SubFields %>
            <% loop SubFields %>
               $EditSegment
            <% end_loop %>
         <% end_if %>
      </ul>
   <% end_if %>

There seems to have been some Javascript modifications made too, but locating the differences between 2.4 and 3.1 is difficult.

Any help is appreciated.