System fields in documents

Currently to express graph structure regarding documents we use fields like "in_", "out_" and so on.
The problem with those fields that they can be accessed by users as result information which should be encapsulated inside documents can be changed by users. It is proposed to introduce the concept of system fields. Let suppose we will have fields which have names, not "in_" but "@in_" for example, those fields can not be accessed by conventional access methods like document.field(). So queries which are used to update and create documents or vertexes like "update/upsert" and so on will not be able to access and modify and damage content of those fields. Those fields will be accessed only in special places like in "in()" function or "create edge" function. The downside of this approach, of course, is that users in their SQL queries always should use graph functions instead of plain fields. But the idea initially was that those fields had to be encapsulated.