Scribble is part of the PLT Scheme distribution as of version 4.0, which was released in June 2008, and all PLT Scheme documentation is created with Scribble. Developing Scribble, porting old PLT Scheme documentation, and writing new documentation took about a year, but the @ notation evolved earlier through years of experimentation.
The documentation at http://docs.plt-scheme.org/ is built nightly by Scribble from a snapshot of the PLT Scheme source repository. The same documentation is available in PDF form at http://pre.plt-scheme.org/docs/pdf/. At the time of this writing, the 70 PDF files of current documentation total 3778 pages in a relatively sparse format, which we estimate would fit in around 1000 pages if compressed into a conference-style, two-column layout. This total includes documentation only for libraries that are bundled with PLT Scheme; additional libraries for download via PLaneT are also documented using Scribble.
PLT Scheme documentation was previously written in LaTeX and converted to HTML via tex2page (Sitaram 2007). Although tex2page was a dramatic improvement over our original use of latex2html, the build process relied on layers of fragile LaTeX macros, HTML hacks, and pre- and post-processing scripts, which made the documentation all but impossible to build except by its authors. Consequently, most library documentation used a plain-text format that was easier to write but inconsistent in style and difficult to index. The documentation index distinguished identifier names from general terms, but it did not attach a source module to each identifier name, so online help relied on textual search.
The Scribble-based documentation system is accessible to all PLT Scheme users, who write their own documentation using Scribble and often supply patches to the main document sources. Scribble produces output that is more consistent and easier to navigate than the old documentation, and the resulting documentation works better with online help. More importantly, the smooth path from API documentation to stand-alone documents has let us produce much more tutorial and overview documentation, helping users find their way through the volumes of available information.