Documentation for setting up the development environment for the Modern UI

hi @Joe Schmucker  - even I got the same issue using the documentation while trying to Execute npm run build-dev
 

any help is appreciated  
CC: @rakeshe45 

@Joe Schmucker or anyone really… Do we know; are we supposed to have the ability to generate custom screens in the modern UI at this point, or are we limited to playing with those that come default under FrontendSources?

Reading the documentation, they use all default screens in their examples, so its unclear to me if they are instructing us only how to recompile default screens after modification or telling us we can do this with any screen and they just use default screens as examples. 

After dealing with a “cross-env is not recognized” error using  npm install --save-dev cross-env  I was able to get   npm run build-dev -- --env screenIds=|custom screen|  to run successfully with no errors, but it didn’t generate the FrontendSoures files for my custom screen. 

I very well may be missing something, but I thought it worth asking the question before I burn time on another 100 derivatives.  

Even if we did have to build the html and ts ourselves, at least there is documentation for that. But there’s still the issue that when you attempt to switch a screen to the Modern UI, the site map is locked down to search for |screenID|.html in the ./Scripts/Screens directory before it ever references the ./FrontendSources files.

The default screens all have corresponding html and js files in the ./Scripts/Screens directory, but there’s no documentation that I’ve found that explains how to generate these for custom screens, which tells me either we’ve not yet been provided with this option yet, or else it’s something that is supposed to be handled programmatically, and I’ve simply botched the deployment.