duplicate top of the jo'au'i language stack.
This obscure feature pushes the current language on the jo'au'i language stack, like a DUP on some RPN calculators. jo'au'inai pops (removes) the language at the top of the stack. Neither switches the language by themselves. «jo'au'i jo'au …» is a call rather than switch to another language (like call vs jump in assembly), and «jo'au'inai jo'au lo galraipau» (if still in Lojban with a dialect that includes jo'au'i) pops back to the outer language. jo'au sets (changes / mutates) the top of the stack; normally the top of the stack is the currently used language, so it is good practice to explicitly switch back to the top of the stack after it is done being manipulated. See also: bau'o (language switch), jo'au (switch to language), zoi'o (quote and language switch). Additionally, see also jo'au'e (shortcut to a push-call language switch (from «nenri»)), jo'au'a (shortcut to a pop back to outer language (from «bartu»)).