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Bikeshed, a spec preprocessor

Bikeshed is a pre-processor for the source documents the CSSWG produces their specs from. We write our specs in HTML, but rely on a preprocessor for a lot of niceties, like automatically generating a bibliography and table of contents, or automatically linking terms to their definitions. Specs also come with a lot of boilerplate repeated on every document, which we omit from our source document.

The processor can be easily installed and run locally (requiring no network access unless you're updating), or accessed as a CGI without any installation at all:

While a few features are specialized for the CSSWG's purposes, Bikeshed should be useful as a general-purpose spec processor.

A short overview of my preprocessor's features:

Examples of much of the functionality described here can be found by looking at the source of the CSS Variables source document

Note About Fatal Errors

Bikeshed generates "fatal errors" for lots of things that it wants you to fix, but generally recovers gracefully from them anyway. If you're getting a fatal error, but don't have time to fix it and just need a spec right now, you can force Bikeshed to generate anyway with the -f flag, like: bikeshed -f spec.

This is also sometimes useful when converting a spec to Bikeshed for the first time, so you can see all the errors at once and fix them in whatever order is easiest, rather than having to deal with them one-by-one with no idea when they'll end. (You may also want to silence the warnings in this case, to reduce visual noise until you've gotten it at least building successfully. Use bikeshed -qf spec.)

Documentation Sections

  • Installing Bikeshed - gets you from "reading this page" to "running Bikeshed" in as few steps as possible.
  • Quick Start Guide - gets you from an empty file to a full spec in no time.
  • Metadata - describes the format of the required metadata block in your spec.
  • Definitions, Autolinks, and Bibliography - describes how to create definitions, autolinks, and bibliography entries.
  • Markup - describes several of the markup niceties and shortcuts over plain HTML that the processor recognizes.
  • Global Names - describes the concept and syntax of global names, which are used by several features to uniquely identify and refer to defined terms.
  • IDL - describes Bikeshed's automatic IDL processing.
  • Railroad Diagrams - describes the railroad-diagram feature, and its syntax.
  • Boilerplate - describes the use and generation of a spec's boilerplate sections. You probably don't need to read this.
  • Source-File Processing - describes the functions Bikeshed has for processing your source file itself.

Bikeshed File Extension

The preferred file extensions for Bikeshed source files is bs, like Bikeshed will automatically recognize *.bs files in the folder it's run in, and assume that you want an output file of the same name with a .html extension. The repository also contains a syntax highlighting script for Bikeshed source files.

(Bikeshed also recognizes files with *.src.html for backwards compatibility with older CSS specs, though most such specs have switched their source file extensions to .bs now. Using .src.html in most text editors will display the file with HTML source formatting, which isn't generally what you want.)


This document and all associated files in the github project are licensed under CC0 . This means you can reuse, remix, or otherwise appropriate this project for your own use without restriction. (The actual legal meaning can be found at the above link.) Don't ask me for permission to use any part of this project, just use it. I would appreciate attribution, but that is not required by the license.


A preprocessor for the CSSWG that converts source files into actual specs.



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