Typing annotations ?

Dear Web Annotations users,

Thank you very much for the 'light speed' answer on the embeded svg
annotation.
It's great that the way of achieving this is so simple...

I have another question regarding typing the annotations.
It's still with embedded bodies.

I'd like to type annotations that would be understood by the annotation
software.

Suppose that I want to tag some piece of text (identified with the target)
with either a specific color or a specific shape.
As there is no property to assign a custom type to an annotation (or I
didn't find one) what would be the proper way to do this ?

I thought of using (suppose I have 2 annotations) :

  "body": [
     {
       "type": "TextualBody",
       "value": "COLOR",
       "purpose": "tagging"
     },
     {
       "type": "TextualBody",
       "value": "blue",
       "purpose": "tagging"
     }
   ],

  "body": [
     {
       "type": "TextualBody",
       "value": "SHAPE",
       "purpose": "tagging"
     },
     {
       "type": "TextualBody",
       "value": "circle",
       "purpose": "tagging"
     }
   ],

The idea behind is also to be able to filter (not show) some annotations of
a particular type...

PS : I used "purpose":"tagging" as it seemed to me the best kind of
annotation in that situation, but that's probably not the main point of my
question.

Thank you in advance.

Best regards.

Etienne.