The obvious answer would be to download the program and decompile it, to see for yourself. Fortunately, StarDict is open-source, GPL'd code.
Why don't you just download the source-code and check it out for yourself?
Much easier than implementing your own custom-control that emulates the appearance of a richedit while thwarting the efforts of any program to retrieve the text for itself.
Source-forge has apparently removed the project due to copyright concerns, though it can still be found via code.google
Here's the download page:
http://code.google.com/p/stardict-3/downloads/list[
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