I don't see any need to escape in this case. The new meta command (!RELATION) in my example has one required argument, which is the relation type. Right now, there are two possible relation types: PARENT and CHILD. The PARENT relation type has no further arguments. The CHILD relation type is required to be followed by a free-form string which acts as the name of the relation. If additions are needed in the future, new relation types can be introduced. Adding other arguments to the existing relation types would just cause problems, so any changes at all would need to be in the form of new types with new names.
For example, if in the future it was decided that PARENT could stand to have a name also, then instead of simply adding a name to the existing PARENT type, a new type would be create that requires a name (like PARENT2, or something).
For example, if in the future it was decided that PARENT could stand to have a name also, then instead of simply adding a name to the existing PARENT type, a new type would be create that requires a name (like PARENT2, or something).