I've got this working pretty nicely now in DF20. I think that I am just about to try to implement it into a DF20 project

It also works pretty good prior to DF20 but does has 2 issues that I have come across. These are NOT an issue in DF20

1. if the text contains accented characters (ie Ascii characters over 127). The RTF control in DF19.0 uses standard RTF special characters (ie é is represented as "\'e9") and these blow up my checking and markup routine. I may create a different routine for DF19 simply because I had my sights on testing this more thoroughly prior to the release of DF20

2. Sometimes the colour red gets lost and the errored text and underline are just shown in black instead of red.

AGAIN, my intention was simply to create a way to allow an end user to enter simple Text (not RichText), so I haven't done too much testing with this as a control that allows the user to enter Rich Text

You can download the newest revision here:
https://www.grasp.ca/dls/GSCSpeller_1.0.03.exe