Abstract:
We revise and extend a couple of earlier incompletely published papers regarding the competence limits of formal systems in modelling the full syntax of programing languages. We show that the full syntax of mainstream programming languages (e.g. similar to Pascal or CAML) and of schema based XML documents cannot be modelled by either ET0L systems or indexed grammars. We raise a few open questions related to ET0L languages and two powerful but less known classes of languages: iterative languages and generalised Ogden-like languages.