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