Add key/value pair extension for flexibility

[RoelantVos]

In some cases, it may be necessary to add specific notes or items to the existing schema in an open format.

The suggestion is to add a key/value object to every segment so that the user can add whatever additional notes he or she deems useful.

The key/value object would be an array, which in the templating engines can be access via the array index.

Structure:

• key
• value
• description