I've renamed this to "body".

About the "location" of the comment, it seems that besides the entity type, id and revision, we also need:
- the field name (e.g. "body")
- the value which is actually used (e.g. "value" or "summary")

Do you agree?
Do you also need to store a position, somehow?

Also note that I didn't include the bundle of the entity, which is generally not useful to pinpoint an entity, but maybe you needed it for another reason?