Add a definition/description field to Accessibility

[Raphael-Gazzotti]

The Accessibility library currently lacks clear guidance on the usage of its different instances. Introducing this field would improve clarity and facilitate their correct use.

[Raphael-Gazzotti]

The use-case should be detailed in this property.
Other options: Purpose/Application/Utility/Intend

[Raphael-Gazzotti]

We will modify the name of this field depending on the text attached to the instances.