See [Ctext] highlighting widget for a complete solution that works well. 

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Also see [Jeffrey Hobbs] ''Tcl source code to HTML compatible format
converter [http://www.tcl.tk/community/hobbs/tcl/script/main.html]''. 
Does some intelligent highlighting.

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See also [Looping over the contents of a text widget] which includes code that lets you supply a pattern and apply a tag to all ranges that match that pattern.
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%| [Category GUI]|[Category syntax] |%
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