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  2
  3Blackfriday
  4===========
  5
  6Blackfriday is a [Markdown][1] processor implemented in [Go][2]. It
  7is paranoid about its input (so you can safely feed it user-supplied
  8data), it is fast, it supports common extensions (tables, smart
  9punctuation substitutions, etc.), and it is safe for all utf-8
 10(unicode) input.
 11
 12HTML output is currently supported, along with Smartypants
 13extensions. An experimental LaTeX output engine is also included.
 14
 15It started as a translation from C of [upskirt][3].
 16
 17
 18Installation
 19------------
 20
 21Blackfriday is compatible with Go 1. If you are using an older
 22release of Go, consider using v1.1 of blackfriday, which was based
 23on the last stable release of Go prior to Go 1. You can find it as a
 24tagged commit on github.
 25
 26With Go 1 and git installed:
 27
 28    go get github.com/russross/blackfriday
 29
 30will download, compile, and install the package into your `$GOPATH`
 31directory hierarchy. Alternatively, you can achieve the same if you
 32import it into a project:
 33
 34    import "github.com/russross/blackfriday"
 35
 36and `go get` without parameters.
 37
 38Usage
 39-----
 40
 41For basic usage, it is as simple as getting your input into a byte
 42slice and calling:
 43
 44    output := blackfriday.MarkdownBasic(input)
 45
 46This renders it with no extensions enabled. To get a more useful
 47feature set, use this instead:
 48
 49    output := blackfriday.MarkdownCommon(input)
 50
 51### Sanitize untrusted content
 52
 53Blackfriday itself does nothing to protect against malicious content. If you are
 54dealing with user-supplied markdown, we recommend running blackfriday's output
 55through HTML sanitizer such as
 56[Bluemonday](https://github.com/microcosm-cc/bluemonday).
 57
 58Here's an example of simple usage of blackfriday together with bluemonday:
 59
 60``` go
 61import (
 62    "github.com/microcosm-cc/bluemonday"
 63    "github.com/russross/blackfriday"
 64)
 65
 66// ...
 67unsafe := blackfriday.MarkdownCommon(input)
 68html := bluemonday.UGCPolicy().Sanitize(string(unsafe))
 69```
 70
 71### Custom options
 72
 73If you want to customize the set of options, first get a renderer
 74(currently either the HTML or LaTeX output engines), then use it to
 75call the more general `Markdown` function. For examples, see the
 76implementations of `MarkdownBasic` and `MarkdownCommon` in
 77`markdown.go`.
 78
 79You can also check out `blackfriday-tool` for a more complete example
 80of how to use it. Download and install it using:
 81
 82    go get github.com/russross/blackfriday-tool
 83
 84This is a simple command-line tool that allows you to process a
 85markdown file using a standalone program.  You can also browse the
 86source directly on github if you are just looking for some example
 87code:
 88
 89* <http://github.com/russross/blackfriday-tool>
 90
 91Note that if you have not already done so, installing
 92`blackfriday-tool` will be sufficient to download and install
 93blackfriday in addition to the tool itself. The tool binary will be
 94installed in `$GOPATH/bin`.  This is a statically-linked binary that
 95can be copied to wherever you need it without worrying about
 96dependencies and library versions.
 97
 98
 99Features
100--------
101
102All features of upskirt are supported, including:
103
104*   **Compatibility**. The Markdown v1.0.3 test suite passes with
105    the `--tidy` option.  Without `--tidy`, the differences are
106    mostly in whitespace and entity escaping, where blackfriday is
107    more consistent and cleaner.
108
109*   **Common extensions**, including table support, fenced code
110    blocks, autolinks, strikethroughs, non-strict emphasis, etc.
111
112*   **Safety**. Blackfriday is paranoid when parsing, making it safe
113    to feed untrusted user input without fear of bad things
114    happening. The test suite stress tests this and there are no
115    known inputs that make it crash.  If you find one, please let me
116    know and send me the input that does it.
117
118    NOTE: "safety" in this context means *runtime safety only*. In order to
119    protect yourself agains JavaScript injection in untrusted content, see
120    [this example](https://github.com/russross/blackfriday#sanitize-untrusted-content).
121
122*   **Fast processing**. It is fast enough to render on-demand in
123    most web applications without having to cache the output.
124
125*   **Thread safety**. You can run multiple parsers in different
126    goroutines without ill effect. There is no dependence on global
127    shared state.
128
129*   **Minimal dependencies**. Blackfriday only depends on standard
130    library packages in Go. The source code is pretty
131    self-contained, so it is easy to add to any project, including
132    Google App Engine projects.
133
134*   **Standards compliant**. Output successfully validates using the
135    W3C validation tool for HTML 4.01 and XHTML 1.0 Transitional.
136
137
138Extensions
139----------
140
141In addition to the standard markdown syntax, this package
142implements the following extensions:
143
144*   **Intra-word emphasis supression**. The `_` character is
145    commonly used inside words when discussing code, so having
146    markdown interpret it as an emphasis command is usually the
147    wrong thing. Blackfriday lets you treat all emphasis markers as
148    normal characters when they occur inside a word.
149
150*   **Tables**. Tables can be created by drawing them in the input
151    using a simple syntax:
152
153    ```
154    Name    | Age
155    --------|------
156    Bob     | 27
157    Alice   | 23
158    ```
159
160*   **Fenced code blocks**. In addition to the normal 4-space
161    indentation to mark code blocks, you can explicitly mark them
162    and supply a language (to make syntax highlighting simple). Just
163    mark it like this:
164
165        ``` go
166        func getTrue() bool {
167            return true
168        }
169        ```
170
171    You can use 3 or more backticks to mark the beginning of the
172    block, and the same number to mark the end of the block.
173
174*   **Autolinking**. Blackfriday can find URLs that have not been
175    explicitly marked as links and turn them into links.
176
177*   **Strikethrough**. Use two tildes (`~~`) to mark text that
178    should be crossed out.
179
180*   **Hard line breaks**. With this extension enabled (it is off by
181    default in the `MarkdownBasic` and `MarkdownCommon` convenience
182    functions), newlines in the input translate into line breaks in
183    the output.
184
185*   **Smart quotes**. Smartypants-style punctuation substitution is
186    supported, turning normal double- and single-quote marks into
187    curly quotes, etc.
188
189*   **LaTeX-style dash parsing** is an additional option, where `--`
190    is translated into `&ndash;`, and `---` is translated into
191    `&mdash;`. This differs from most smartypants processors, which
192    turn a single hyphen into an ndash and a double hyphen into an
193    mdash.
194
195*   **Smart fractions**, where anything that looks like a fraction
196    is translated into suitable HTML (instead of just a few special
197    cases like most smartypant processors). For example, `4/5`
198    becomes `<sup>4</sup>&frasl;<sub>5</sub>`, which renders as
199    <sup>4</sup>&frasl;<sub>5</sub>.
200
201
202Other renderers
203---------------
204
205Blackfriday is structured to allow alternative rendering engines. Here
206are a few of note:
207
208*   [github_flavored_markdown](https://godoc.org/github.com/shurcooL/go/github_flavored_markdown):
209    provides a GitHub Flavored Markdown renderer with fenced code block
210    highlighting, clickable header anchor links.
211
212    It's not customizable, and its goal is to produce HTML output
213    equivalent to the [GitHub Markdown API endpoint](https://developer.github.com/v3/markdown/#render-a-markdown-document-in-raw-mode),
214    except the rendering is performed locally.
215
216*   [markdownfmt](https://github.com/shurcooL/markdownfmt): like gofmt,
217    but for markdown.
218
219*   LaTeX output: renders output as LaTeX. This is currently part of the
220    main Blackfriday repository, but may be split into its own project
221    in the future. If you are interested in owning and maintaining the
222    LaTeX output component, please be in touch.
223
224    It renders some basic documents, but is only experimental at this
225    point. In particular, it does not do any inline escaping, so input
226    that happens to look like LaTeX code will be passed through without
227    modification.
228
229
230Todo
231----
232
233*   More unit testing
234*   Markdown pretty-printer output engine
235*   Improve unicode support. It does not understand all unicode
236    rules (about what constitutes a letter, a punctuation symbol,
237    etc.), so it may fail to detect word boundaries correctly in
238    some instances. It is safe on all utf-8 input.
239
240
241License
242-------
243
244Blackfriday is distributed under the Simplified BSD License:
245
246> Copyright © 2011 Russ Ross
247> All rights reserved.
248> 
249> Redistribution and use in source and binary forms, with or without
250> modification, are permitted provided that the following conditions
251> are met:
252> 
253> 1.  Redistributions of source code must retain the above copyright
254>     notice, this list of conditions and the following disclaimer.
255> 
256> 2.  Redistributions in binary form must reproduce the above
257>     copyright notice, this list of conditions and the following
258>     disclaimer in the documentation and/or other materials provided with
259>     the distribution.
260> 
261> THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
262> "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
263> LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
264> FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
265> COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
266> INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
267> BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
268> LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
269> CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
270> LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
271> ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
272> POSSIBILITY OF SUCH DAMAGE.
273
274
275   [1]: http://daringfireball.net/projects/markdown/ "Markdown"
276   [2]: http://golang.org/ "Go Language"
277   [3]: http://github.com/tanoku/upskirt "Upskirt"