Question for the others: What's the difference of \dodoubleargument and \dodoubleempty? I expected \dodoubleargument to throw an error since the arguments are supposed to be mandatory.
In MkIV Hans didn’t add this check and in MkII he disabled is for command with three or less argument but even then you get only a message in the log when your command has no argument (i.e. a command with four argument complains only when it has zero argument but doesn’t complain when it has one to four arguments).
Wikified: http://wiki.contextgarden.net/Command/dodoubleempty (I've been meaning to document that command for a while now. As a complement to the existing explanation at http://wiki.contextgarden.net/Commands_with_optional_arguments, I mean.) --Sietse