Metalanguage = object formal language in semantic brackets.
Example of semantic brackets in character strings is using a special character which is never used in the object language.
As the number of characters is very limited, the special character is often an unused string of characters, like : = ,
http://www , Ctrl Z, [/quote] and [quote], etc.
Building an object language vs metalanguage may use different gramatic too but it is not mandatory.
Children playing to be master or parents or king mostly build metalanguage to be considered as master, parents or king! Sometimes they forget to use the metalanguage and suddenly they are no more king, and everybody is laughing.
In the simulator a hidden mistake (forget the space between ":" and "=" and you discover a smiley no-no instead of the string ": =" ) in the metalanguage semantic brackets may modify the behaviour of the simulated system (plane, inertial system, aso) without you know it, and you have a bad surprise when you do the same action on the plane, despite your aerodynamic algorithm is OK.
It is always difficult to test the semantic brackets, you would mostly need a meta-meta-language!
All that applies well on well structured simple systems using formal language. Graceful degradation brings a greater complexity .... KISS!