XML is a language for defining grammars for mark-up languages.
There will be a big need to translate between different
mark-up languages that carry similar information.

This project is about specifying the language translations
at a high-level of abstraction without talking about the details
of the source and target language grammars.

Example:

A -> B bypassing {A} = A -> B bypassing A
A -> A -> B bypassing {A} = A -> A -> B bypassing {A}
...
A -> n times -> A -> B bypassing {A} = A -> n times -> A -> B bypassing {A}

means: if there is a B-object at nesting level n in the source then
the same B-object exists at nesting level n in the translated 
object.

A -> Y bypassing {A} -> C bypassing {A} = 
A -> C bypassing {A} = 

A -> A bypassing A -> Y bypassing {A} -> C bypassing {A} = 
A -> A bypassing A -> C bypassing {A} 
...
A -> n times -> A bypassing A -> Y bypassing {A} -> C bypassing {A} =
A -> n times -> A bypassing A -> C bypassing {A}

means: only the C-objects reachable through Y are translated.
if there is a C-object at nesting level n in the source then
the same C-object exists at nesting level n in the translated 
object.

grammar 1:

A = R Y Q.
R = S.
S = B.
Y = C.
Q = C.
C = [A].
B = .

grammar 2:

A = R1 X.
R1 = S1.
S1 = R.
R = S.
S = B.
X = C.
C = [A].
B = .

The translation works as follows:
Retrieve the outermost B-object from object 1 of grammar 1.
Retrieve the outermost C-object from object 1 (reachable trough Y).
Create an A-object (object 2) of grammar 2 (assuming [A] absent)
and put B-object fom object 1 in.