Check out some of the examples installed with PSPad in the Syntax subdirectory. I'm not familiar with REBOL but maybe you can find a similar language listed to get you started. I created a syntax highlighter for DIBOL, which I'm sure is not similar, by finding something similar and viewing what shows up in the Settings->User Highlighter menu. I copied keywords out of an electronic programming manual and pasted them in for starters.
-- <http://forum.pspad.com/read.php?2,36507,36551> PSPad freeware editor http://www.pspad.com
