One of the first, larger C++ plugin projects for 3ds Max i started from the ground up was MXSEditor in 2011. This plugin exposes the complete maxscript editor and it’s internal Scintilla/SciTe text editor components to maxscript. Features include operating the maxscript editor in an extended viewport, extensive control over the maxscript editor via maxscript and as mentioned, complete access to the Scintilla/SciTe command set (see Scintilla Documentation )

In 2012, the project hit a a major roadblock when Autodesk switched 3ds Max code over to unicode ( starting with Max 2013 ). A necessary step every plugin developer had to follow in turn. Working around this and updating the code  was a major undertaking for MXSEditor, as it mainly uses  strings internally and in its maxscript interface.  But now it’s done and i soon will release an updated plugin package, supporting from Max 2008 up to Max 2017, x86 and x64 alike.

Currently documentation is in the works, as previously people didn’t fully grasp the scope of this plugin’s application

In the meantime, you simply can watch an updated demo about how  realtime-audio drives the  editor selection demo