It is invalid to use variables in path expressions and while this does fail, the error message is not what would be expected.

[error] Schema Definition Error: Unable to parse expression. Message: `}' expected but `/' found

See tests:
test_var_in_path
test_var_end_path

In files:
daffodil-test/src/test/resources/edu/illinois/ncsa/daffodil/section07/variables/variables.tdml
daffodil-test/src/test/scala-debug/edu/illinois/ncsa/daffodil/section07/variables/TestVariablesDebug.scala