The old e-mail and Usenet news convention is to use _italics_ and *boldface*.
Dolphin WikiWeb uses those conventions: http://www.object-arts.com/wiki/html/Dolphin/WikiTextFormattingRules.htm
I can't find the reference that explains his rationale, but I seem to recall that Ward created ''italic'' and '''bold''' because those markups were easily distinguishable and trivial to type. Both _ and * require the use of the shift key, and that didn't meet with his objective to make content creation as easy as possible. Of course, that doesn't explain why he settled on CamelCase, but I think it's safe to say that CamelCase betrays the influence of his object-oriented coding background. (CamelCase is more popular than underscores_in_variables among OO types.) I, for one, am extremely grateful to Cliff Adams for inventing the [[free link]] convention. Easy to distinguish from plain text, easy to type, and it's more aesthetically pleasing and flexible.
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