Command sub-directives not handled correctly
Firstly, I would have expected <TAB> to indent for each sub-directive. In any case, when one adds leading whitespace as stated in the manual font-locking is applied as expected to each of the sub-directives except for the alias sub-directive of the commodity command directive. Font locking is applied to the alias sub-directive of the payee command directive and when it is used as a command directive to define an account alias.
Another issue, is when one hits RET after entering a sub-directive. This has the effect at least for me to remove the indentation of the sub-directive and font-locking is removed as one would expect for all except the alias sub-directive but that is only because it is now the command directive rather than the sub-directive. I would have expected RET to move to the next line but respect the indentation of the previous sub-directive line.