The triple script dialect is carefully designed such that every valid triple script (i.e. post-compilation form) is syntactically valid for any compliant ECMA-262 parser. (However, be aware that this is not JavaScript.)
For the time being, the pre-compilation form for triple script modules also happens to be similarly syntactically valid, but there is no long-term commitment to maintain this property. (Although there is such a commitment regarding the post-compilation. Any other stance would obviate triplescripts.org reason to exist.)
There is no formal grammar at this time. The triplescripts.org reference compiler trplkt is currently pre-1.0. As we work towards standardization, it's extremely likely that the triple script dialect implemented in future compiler versions will break programs written for earlier versions while the compiler has not reached 1.0. Neither trplkt itself nor any other triplescripts.org project is guaranteed to be be free of errors that would prevent them from being broken. However, we are committed to stability after 1.0, with the option to break backwards compatibility in 2.0 (if we ever reach that point; the work of this group is expected to be low-churn once 1.0 is reached).