placeholder for the last returned valueIn Mathematica, one can use "%" as a placeholder for the last returned value.

Is there something similar in JMP?
Then one could use the fact that a reference to an object is returned by the function which creates the object.
Could help during debugging:
Run single lines of the original code, add some test code and get a quick reference to a created object via the placeholder.
Names Default to Here(1);
dt = Open( "$SAMPLE_DATA/Big Class.jmp" );
dt << Graph Builder(
Size( 437, 413 ),
Graph Spacing( 4 ),
Variables( X( :height ), Y( :weight ), Overlay( :sex ) ),
Elements( Points( X, Y, Legend( 1 ) ), Smoother( X, Y, Legend( 2 ) ) )
);
// during debugging:
gb = %;(gb << XPath( "//AxisBox" )) << select;<BR /><BR />// or even better:
gb << get XML();
New Window("xml", %)
Advanced Statistical ModelingConsumer and Market ResearchRe: placeholder for the last returned valueInteresting idea, I kudo'd your wish list item.
I usually work around the absence of this by nesting more things into each other...but it can become difficult to read:
Names Default to Here(1);
dt = Open( "$SAMPLE_DATA/Big Class.jmp" );
gb = dt << Graph Builder(
Size( 437, 413 ),
Graph Spacing( 4 ),
Variables( X( :height ), Y( :weight ), Overlay( :sex ) ),
Elements( Points( X, Y, Legend( 1 ) ), Smoother( X, Y, Legend( 2 ) ) )
);
CapturedXML = gb << XPath( "//AxisBox" )[1] << get xml; //Like so
Re: placeholder for the last returned valueI posted a wish :
https://community.jmp.com/t5/JMP-Wish-List/JSL-debugging-placeholder-for-last-returned-value/idi-p/568705
and added another example in the code above.
Let's see if other users are also interested ...
sure: If you had this comfort in Mathematica, you kind of miss it in JMP.
Could be that you don't miss it if you didn't have it 
Re: placeholder for the last returned valueNo, there is no way to retrieve the value. You could move the "gb =" to just before the "dt<