The Pillar syntax is a wiki like syntax extracted by Damien Cassou from the Pier content management system. The Pillar project offers transformers into several target formats such as LaTeX, html or markdown.
J.F. Rick writes on the Pharo development list about the Pillar syntax
Wed, Jul 2, 2014 at 12:05 PM
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Back in 1999, I created ComSwiki out of the beginning that was PWS Swiki (the first wiki to eschew camel case for links). One of the first things I did was to make changes to the markup to improve it. Of course, once we had some users and established content, all the decisions I made at that early point in the project were made permanent.
Looking at Pillar, it pretty much uses the syntax I created back then (with a few improvements).
I'm sure the markup just drifted through the Smalltalk community and was then adopted by Pillar. It's not a bad design but I've always felt that a better, more extensible syntax was possible. As usual, the good proved to be the enemy of the great.