GUI indicator for a command environment

[Paul A. Rubin]

Dear devs,

I'm struggling to cobble together a module supporting the pseudocode 
features of the algorithmicx package. As a disclaimer, I'm trying to 
avoid flex insets and stick to environments as much as possible, because 
there's less mousery switching an environment than insert an inset.

Right now, I'm tripping over the for block, which it implements by two 
LaTeX commands: \For{<conditions>} and \EndFor. I can treat those as 
command styles and get the correct output, but the GUI is confusing to 
the user because nothing displays in the line ending the loop (it looks 
like a blank line to the user) and the condition appears in the starting 
line with no visible prefix (so it looks like any random statement in 
the algorithm, unless you notice what the environment select box is 
displaying.

So what I'm looking for right now is a way to display a 
tag/prefix/symbol at the start of a command style that appears in the 
GUI but /not/ in the compiled output. The "handle" for an inset would be 
fine, as would something like a bullet that was GUI-only. Can this be 
done with the current layout/module system?

TIA,
Paul