Sgmltexi is an SGML system (DTD and tools) to make Texinfo documentation using SGML. The Sgmltexi DTD is designed to follow most of the Texinfo philosofy, hiding the node managing.
Sgmltexi is to be intended as a simplified Texinfo using SGML; that is: you cannot do all that it is possible with Texinfo alone. Sgmltexi impose some restrictions, but maybe it can be simpler to write Texinfo documentation this way.