It would be useful if the FreeMarker pcString tag were to report an error if a tag was not parsed, i.e. it was not a valid export tag. Ideally this would also stop output so that the errors could not be ignored.
Both pcstring and pcboolean now will stop the output if an invalid tag is encountered. This highlighted some invalid tags in the existing base exports (unit test and normal pdf) which have now been fixed.
pcvar is not able to detect invalid syntax as it uses the variable system, which silently defaults any error responses to a 0 result.