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authorJohn MacFarlane <jgm@berkeley.edu>2014-08-13 22:28:18 -0700
committerJohn MacFarlane <jgm@berkeley.edu>2014-08-13 22:56:33 -0700
commit5cff19421421948a32382b7c046841eb7a62c992 (patch)
tree5f460164bdb19c0ee77535b75f79d6fb7b1021a8 /README.md
parent84bad7440033ced38f8dfba1f839a6966fc88a5e (diff)
Fleshed out README.
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@@ -1,27 +1,37 @@
Standard markdown
=================
-Standard markdown is a specification of markdown syntax, together
-with implementations (`stmd`) in C and javascript.
+Standard markdown is a specification of markdown syntax, together with
+implementations (`stmd`) in C and javascript.
+
+The implementations
+-------------------
The C implementation provides both a library and a standalone program
-that converts markdown to HTML. It is written in standard C99 and has
-no library dependencies. (However, if you check it out from the
+`stmd` that converts markdown to HTML. It is written in standard C99
+and has no library dependencies. (However, if you check it out from the
repository, you'll need `re2c` to generate `scanners.c` from
`scanners.re`. This is only a build dependency for developers, since
`scanners.c` can be provided in a released source tarball.)
-The javascript implementation is a single javascript file
-that can be linked to an HTML page. A standalone version (using
-`node.js`) is also provided (`js/markdown`), and there is a
-"dingus" for playing with it interactively. (`make dingus` will start
+ Usage: stmd [FILE*]
+ Options: --help, -h Print usage information
+ --ast Print AST instead of HTML
+ --version Print version
+
+The javascript implementation is a single javascript file, with
+no dependencies, that can be linked to in an HTML page. A standalone
+version (using `node.js`) is also provided (`js/markdown`), and there is
+a "dingus" for playing with it interactively. (`make dingus` will start
this.)
-The spec contains over 400 embedded examples which serve as
-conformance tests. To run the tests for `stmd`, do `make test`.
-To run them for another markdown program, say `myprog`,
-do `make test PROG=myprog`. To run the tests for `stmd.js`,
-do `make testjs`.
+The spec contains over 400 embedded examples which serve as conformance
+tests. To run the tests for `stmd`, do `make test`. To run them for
+another markdown program, say `myprog`, do `make test PROG=myprog`. To
+run the tests for `stmd.js`, do `make testjs`.
+
+The spec
+--------
The source of the spec is `spec.txt`. This is basically a markdown
file, with code examples written in a shorthand form:
@@ -32,8 +42,51 @@ file, with code examples written in a shorthand form:
expected HTML output
.
-To build an HTML version of the spec, do `make spec.html`.
-To build a PDF version, do `make spec.pdf`. Both these commands
-require that pandoc is installed, and creating a PDF requires
-a latex installation.
+To build an HTML version of the spec, do `make spec.html`. To build a
+PDF version, do `make spec.pdf`. Both these commands require that
+pandoc is installed, and creating a PDF requires a latex installation.
+
+The spec is written from the point of view of the human writer, not
+the computer reader. It is not an algorithm---an English translation of
+a computer program---but a declarative description of what counts as a block
+quote, a code block, and each of the other structural elements that can
+make up a markdown document.
+
+Because John Gruber's [canonical syntax
+description](http://daringfireball.net/projects/markdown/syntax) leaves
+many aspects of the syntax undetermined, writing a precise spec requires
+making a large number of decisions, many of them somewhat arbitrary.
+In making them, I have appealed to existing conventions and
+considerations of simplicity, readability, expressive power, and
+consistency. I have tried to ensure that "normal" documents in the many
+incompatible existing implementations of markdown will render, as far as
+possible, as their authors intended. And I have tried to make the rules
+for different elements work together harmoniously. In places where
+different decisions could have been made (for example, the rules
+governing list indentation), I have explained the rationale for
+my choices. In a few cases, I have departed slightly from the canonical
+syntax description, in ways that I think further the goals of markdown
+as stated in that description.
+
+For the most part, I have limited myself to the basic elements
+described in Gruber's canonical syntax description, eschewing extensions
+like footnotes and definition lists. It is important to get the core
+right before considering such things. However, I have included a visible
+syntax for line breaks and fenced code blocks.
+
+In all of this, I have been guided by eight years experience writing
+markdown implementations in several languages, including the first
+markdown parser not based on regular expression substitutions
+([pandoc](http://github.com/jgm/pandoc) and the first markdown parsers
+based on PEG grammars
+([peg-markdown](http://github.com/jgm/peg-markdown),
+[lunamark](http://github.com/jgm/lunamark). Maintaining these projects
+and responding to years of user feedback have given me a good sense of
+the complexities involved in parsing markdown, and of the various design
+decisions that can be made. I have also explored differences between
+markdown implementations extensively using [babelmark
+2](http://johnmacfarlane.net/babelmark2/). In the early phases of
+working out the spec, I benefited greatly from collaboration with David
+Greenspan, and from feedback from several industrial users of markdown,
+including Jeff Atwood, Vincent Marti, and Neil Williams.