Add a element DOM id class

By default it uses the elements name and its position on the page.
If the element is nested in a parent element it prefixes the id with the parent elements `dom_id`.

Register your own dom id class with

```rb
Alchemy::Element.dom_id_class = MyDomIdClass
```

app/models/alchemy/element.rb

@@ -143,6 +143,18 @@ def new(attributes = {})
         super(element_definition.merge(element_attributes).except(*FORBIDDEN_DEFINITION_ATTRIBUTES))
       end
 
+      # The class responsible for the +dom_id+ of elements.
+      # Defaults to +Alchemy::Element::DomId+.
+      def dom_id_class
+        @_dom_id_class || DomId
+      end
+
+      # Register a custom +DomId+ class responsible for the +dom_id+ of elements.
+      # Defaults to +Alchemy::Element::DomId+.
+      def dom_id_class=(klass)
+        @_dom_id_class = klass
+      end
+
       # This methods does a copy of source and all depending contents and all of their depending essences.
       #
       # == Options

app/models/alchemy/element/dom_id.rb

@@ -0,0 +1,28 @@
+module Alchemy
+  # Returns a dom id used for elements html id tag.
+  #
+  # Uses the elements name and its position on the page.
+  # If the element is nested in a parent element it prefixes
+  # the id with the parent elements dom_id.
+  #
+  # Register your own dom id class with
+  #
+  #  Alchemy::Element.dom_id_class = MyDomIdClass
+  #
+  class Element < BaseRecord
+    class DomId
+      def initialize(element)
+        @element = element
+        @parent_element = element.parent_element
+      end
+
+      def call
+        [parent_element&.dom_id, element.name, element.position].compact.join("-")
+      end
+
+      private
+
+      attr_reader :element, :parent_element
+    end
+  end
+end

app/models/alchemy/element/presenters.rb

@@ -82,7 +82,7 @@ def display_name_with_preview_text(maxlength = 30)
       # Returns a dom id used for elements html id tag.
       #
       def dom_id
-        [parent_element&.dom_id, name, position].compact.join("-")
+        self.class.dom_id_class.new(self).call
       end
 
       # The content that's used for element's preview text.

spec/models/alchemy/element_spec.rb

@@ -151,6 +151,27 @@ module Alchemy
       end
     end
 
+    describe ".dom_id_class" do
+      it "defaults to Alchemy::Element::DomId" do
+        expect(described_class.dom_id_class).to eq(Alchemy::Element::DomId)
+      end
+    end
+
+    describe ".dom_id_class=" do
+      let(:dummy_dom_id) { Class.new }
+
+      around do |example|
+        default_class = described_class.dom_id_class
+        described_class.dom_id_class = dummy_dom_id
+        example.run
+        described_class.dom_id_class = default_class
+      end
+
+      it "sets the dom id class" do
+        expect(described_class.dom_id_class).to eq(dummy_dom_id)
+      end
+    end
+
     describe ".copy" do
       subject { Element.copy(element) }