One good thing about the fields schema xml is that SharePoint will not complain if you define your own attributes … well almost not complain.
So this means you can extend the fields definition and add your own properties of the fields which gives a great power to your SharePoint solutions.
Group=“My Solution Group“
DisplayName=“Business Unit Name“
The only important bit is to use a custom namespace prefix for your custom attributes as if you don’t do so your feature will fail the schema validation when you try to activate it. So simply define your namespace in the Elements element.
And finally to read the values of the custom attributes of your fields you will have to go via the SPField.SchemaXml property, parse the XML and read the value.
I will leave it to your imagination to think about all the powerful things you can implement by extending your field attributes.