text: Blackfriday
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  ===========
  
  Blackfriday is a [Markdown][1] processor implemented in [Go][2]. It
  is paranoid about its input (so you can safely feed it user-supplied
  data), it is fast, it supports common extensions (tables, smart
  punctuation substitutions, etc.), and it is safe for all utf-8
  (unicode) input.
  
  HTML output is currently supported, along with Smartypants
  extensions.
  
  It started as a translation from C of [Sundown][3].
  
  
  Installation
  ------------
  
  Blackfriday is compatible with any modern Go release. With Go and git installed:
  
      go get -u gopkg.in/russross/blackfriday.v2
  
  will download, compile, and install the package into your `$GOPATH` directory
  hierarchy.
  
  
  Versions
  --------
  
  Currently maintained and recommended version of Blackfriday is `v2`. It's being
  developed on its own branch: https://github.com/russross/blackfriday/tree/v2 and the
  documentation is available at
  https://godoc.org/gopkg.in/russross/blackfriday.v2.
  
  It is `go get`-able via [gopkg.in][6] at `gopkg.in/russross/blackfriday.v2`,
  but we highly recommend using package management tool like [dep][7] or
  [Glide][8] and make use of semantic versioning. With package management you
  should import `github.com/russross/blackfriday` and specify that you're using
  version 2.0.0.
  
  Version 2 offers a number of improvements over v1:
  
  * Cleaned up API
  * A separate call to [`Parse`][4], which produces an abstract syntax tree for
    the document
  * Latest bug fixes
  * Flexibility to easily add your own rendering extensions
  
  Potential drawbacks:
  
  * Our benchmarks show v2 to be slightly slower than v1. Currently in the
    ballpark of around 15%.
  * API breakage. If you can't afford modifying your code to adhere to the new API
    and don't care too much about the new features, v2 is probably not for you.
  * Several bug fixes are trailing behind and still need to be forward-ported to
    v2. See issue [#348](https://github.com/russross/blackfriday/issues/348) for
    tracking.
  
  If you are still interested in the legacy `v1`, you can import it from
  `github.com/russross/blackfriday`. Documentation for the legacy v1 can be found
  here: https://godoc.org/github.com/russross/blackfriday
  
  ### Known issue with `dep`
  
  There is a known problem with using Blackfriday v1 _transitively_ and `dep`.
  Currently `dep` prioritizes semver versions over anything else, and picks the
  latest one, plus it does not apply a `[[constraint]]` specifier to transitively
  pulled in packages. So if you're using something that uses Blackfriday v1, but
  that something does not use `dep` yet, you will get Blackfriday v2 pulled in and
  your first dependency will fail to build.
  
  There are couple of fixes for it, documented here:
  https://github.com/golang/dep/blob/master/docs/FAQ.md#how-do-i-constrain-a-transitive-dependencys-version
  
  Meanwhile, `dep` team is working on a more general solution to the constraints
  on transitive dependencies problem: https://github.com/golang/dep/issues/1124.
  
  
  Usage
  -----
  
  ### v1
  
  For basic usage, it is as simple as getting your input into a byte
  slice and calling:
  
      output := blackfriday.MarkdownBasic(input)
  
  This renders it with no extensions enabled. To get a more useful
  feature set, use this instead:
  
      output := blackfriday.MarkdownCommon(input)
  
  ### v2
  
  For the most sensible markdown processing, it is as simple as getting your input
  into a byte slice and calling:
  
  ```go
  output := blackfriday.Run(input)
  ```
  
  Your input will be parsed and the output rendered with a set of most popular
  extensions enabled. If you want the most basic feature set, corresponding with
  the bare Markdown specification, use:
  
  ```go
  output := blackfriday.Run(input, blackfriday.WithNoExtensions())
  ```
  
  ### Sanitize untrusted content
  
  Blackfriday itself does nothing to protect against malicious content. If you are
  dealing with user-supplied markdown, we recommend running Blackfriday's output
  through HTML sanitizer such as [Bluemonday][5].
  
  Here's an example of simple usage of Blackfriday together with Bluemonday:
  
  ```go
  import (
      "github.com/microcosm-cc/bluemonday"
      "gopkg.in/russross/blackfriday.v2"
  )
  
  // ...
  unsafe := blackfriday.Run(input)
  html := bluemonday.UGCPolicy().SanitizeBytes(unsafe)
  ```
  
  ### Custom options, v1
  
  If you want to customize the set of options, first get a renderer
  (currently only the HTML output engine), then use it to
  call the more general `Markdown` function. For examples, see the
  implementations of `MarkdownBasic` and `MarkdownCommon` in
  `markdown.go`.
  
  ### Custom options, v2
  
  If you want to customize the set of options, use `blackfriday.WithExtensions`,
  `blackfriday.WithRenderer` and `blackfriday.WithRefOverride`.
  
  ### `blackfriday-tool`
  
  You can also check out `blackfriday-tool` for a more complete example
  of how to use it. Download and install it using:
  
      go get github.com/russross/blackfriday-tool
  
  This is a simple command-line tool that allows you to process a
  markdown file using a standalone program.  You can also browse the
  source directly on github if you are just looking for some example
  code:
  
  * <http://github.com/russross/blackfriday-tool>
  
  Note that if you have not already done so, installing
  `blackfriday-tool` will be sufficient to download and install
  blackfriday in addition to the tool itself. The tool binary will be
  installed in `$GOPATH/bin`.  This is a statically-linked binary that
  can be copied to wherever you need it without worrying about
  dependencies and library versions.
  
  ### Sanitized anchor names
  
  Blackfriday includes an algorithm for creating sanitized anchor names
  corresponding to a given input text. This algorithm is used to create
  anchors for headings when `EXTENSION_AUTO_HEADER_IDS` is enabled. The
  algorithm has a specification, so that other packages can create
  compatible anchor names and links to those anchors.
  
  The specification is located at https://godoc.org/github.com/russross/blackfriday#hdr-Sanitized_Anchor_Names.
  
  [`SanitizedAnchorName`](https://godoc.org/github.com/russross/blackfriday#SanitizedAnchorName) exposes this functionality, and can be used to
  create compatible links to the anchor names generated by blackfriday.
  This algorithm is also implemented in a small standalone package at
  [`github.com/shurcooL/sanitized_anchor_name`](https://godoc.org/github.com/shurcooL/sanitized_anchor_name). It can be useful for clients
  that want a small package and don't need full functionality of blackfriday.
  
  
  Features
  --------
  
  All features of Sundown are supported, including:
  
  *   **Compatibility**. The Markdown v1.0.3 test suite passes with
      the `--tidy` option.  Without `--tidy`, the differences are
      mostly in whitespace and entity escaping, where blackfriday is
      more consistent and cleaner.
  
  *   **Common extensions**, including table support, fenced code
      blocks, autolinks, strikethroughs, non-strict emphasis, etc.
  
  *   **Safety**. Blackfriday is paranoid when parsing, making it safe
      to feed untrusted user input without fear of bad things
      happening. The test suite stress tests this and there are no
      known inputs that make it crash.  If you find one, please let me
      know and send me the input that does it.
  
      NOTE: "safety" in this context means *runtime safety only*. In order to
      protect yourself against JavaScript injection in untrusted content, see
      [this example](https://github.com/russross/blackfriday#sanitize-untrusted-content).
  
  *   **Fast processing**. It is fast enough to render on-demand in
      most web applications without having to cache the output.
  
  *   **Thread safety**. You can run multiple parsers in different
      goroutines without ill effect. There is no dependence on global
      shared state.
  
  *   **Minimal dependencies**. Blackfriday only depends on standard
      library packages in Go. The source code is pretty
      self-contained, so it is easy to add to any project, including
      Google App Engine projects.
  
  *   **Standards compliant**. Output successfully validates using the
      W3C validation tool for HTML 4.01 and XHTML 1.0 Transitional.
  
  
  Extensions
  ----------
  
  In addition to the standard markdown syntax, this package
  implements the following extensions:
  
  *   **Intra-word emphasis supression**. The `_` character is
      commonly used inside words when discussing code, so having
      markdown interpret it as an emphasis command is usually the
      wrong thing. Blackfriday lets you treat all emphasis markers as
      normal characters when they occur inside a word.
  
  *   **Tables**. Tables can be created by drawing them in the input
      using a simple syntax:
  
      ```
      Name    | Age
      --------|------
      Bob     | 27
      Alice   | 23
      ```
  
  *   **Fenced code blocks**. In addition to the normal 4-space
      indentation to mark code blocks, you can explicitly mark them
      and supply a language (to make syntax highlighting simple). Just
      mark it like this:
  
          ``` go
          func getTrue() bool {
              return true
          }
          ```
  
      You can use 3 or more backticks to mark the beginning of the
      block, and the same number to mark the end of the block.
  
      To preserve classes of fenced code blocks while using the bluemonday
      HTML sanitizer, use the following policy:
  
      ``` go
      p := bluemonday.UGCPolicy()
      p.AllowAttrs("class").Matching(regexp.MustCompile("^language-[a-zA-Z0-9]+$")).OnElements("code")
      html := p.SanitizeBytes(unsafe)
      ```
  
  *   **Definition lists**. A simple definition list is made of a single-line
      term followed by a colon and the definition for that term.
  
          Cat
          : Fluffy animal everyone likes
          
          Internet
          : Vector of transmission for pictures of cats
  
      Terms must be separated from the previous definition by a blank line.
  
  *   **Footnotes**. A marker in the text that will become a superscript number;
      a footnote definition that will be placed in a list of footnotes at the
      end of the document. A footnote looks like this:
  
          This is a footnote.[^1]
          
          [^1]: the footnote text.
  
  *   **Autolinking**. Blackfriday can find URLs that have not been
      explicitly marked as links and turn them into links.
  
  *   **Strikethrough**. Use two tildes (`~~`) to mark text that
      should be crossed out.
  
  *   **Hard line breaks**. With this extension enabled (it is off by
      default in the `MarkdownBasic` and `MarkdownCommon` convenience
      functions), newlines in the input translate into line breaks in
      the output.
  
  *   **Smart quotes**. Smartypants-style punctuation substitution is
      supported, turning normal double- and single-quote marks into
      curly quotes, etc.
  
  *   **LaTeX-style dash parsing** is an additional option, where `--`
      is translated into `&ndash;`, and `---` is translated into
      `&mdash;`. This differs from most smartypants processors, which
      turn a single hyphen into an ndash and a double hyphen into an
      mdash.
  
  *   **Smart fractions**, where anything that looks like a fraction
      is translated into suitable HTML (instead of just a few special
      cases like most smartypant processors). For example, `4/5`
      becomes `<sup>4</sup>&frasl;<sub>5</sub>`, which renders as
      <sup>4</sup>&frasl;<sub>5</sub>.
  
  
  Other renderers
  ---------------
  
  Blackfriday is structured to allow alternative rendering engines. Here
  are a few of note:
  
  *   [github_flavored_markdown](https://godoc.org/github.com/shurcooL/github_flavored_markdown):
      provides a GitHub Flavored Markdown renderer with fenced code block
      highlighting, clickable heading anchor links.
  
      It's not customizable, and its goal is to produce HTML output
      equivalent to the [GitHub Markdown API endpoint](https://developer.github.com/v3/markdown/#render-a-markdown-document-in-raw-mode),
      except the rendering is performed locally.
  
  *   [markdownfmt](https://github.com/shurcooL/markdownfmt): like gofmt,
      but for markdown.
  
  *   [LaTeX output](https://bitbucket.org/ambrevar/blackfriday-latex):
      renders output as LaTeX.
  
  *   [bfchroma](https://github.com/Depado/bfchroma/): provides convenience
      integration with the [Chroma](https://github.com/alecthomas/chroma) code
      highlighting library. bfchroma is only compatible with v2 of Blackfriday and
      provides a drop-in renderer ready to use with Blackfriday, as well as
      options and means for further customization.
  
  
  TODO
  ----
  
  *   More unit testing
  *   Improve Unicode support. It does not understand all Unicode
      rules (about what constitutes a letter, a punctuation symbol,
      etc.), so it may fail to detect word boundaries correctly in
      some instances. It is safe on all UTF-8 input.
  
  
  License
  -------
  
  [Blackfriday is distributed under the Simplified BSD License](LICENSE.txt)
  
  
     [1]: https://daringfireball.net/projects/markdown/ "Markdown"
     [2]: https://golang.org/ "Go Language"
     [3]: https://github.com/vmg/sundown "Sundown"
     [4]: https://godoc.org/gopkg.in/russross/blackfriday.v2#Parse "Parse func"
     [5]: https://github.com/microcosm-cc/bluemonday "Bluemonday"
     [6]: https://labix.org/gopkg.in "gopkg.in"
     [7]: https://github.com/golang/dep/ "dep"
     [8]: https://github.com/Masterminds/glide "Glide"
  
     [BuildSVG]: https://travis-ci.org/russross/blackfriday.svg?branch=master
     [BuildURL]: https://travis-ci.org/russross/blackfriday
     [GodocV2SVG]: https://godoc.org/gopkg.in/russross/blackfriday.v2?status.svg
     [GodocV2URL]: https://godoc.org/gopkg.in/russross/blackfriday.v2
  