# Introduction to GFM

GitHub uses what we're calling "GitHub Flavored Markdown" (GFM) for messages, issues, and comments. It differs from standard Markdown (SM) in a few significant ways and adds some additional functionality.

If you're not already familiar with Markdown, you should spend 15 minutes and go over the excellent [Markdown Syntax Guide](http://daringfireball.net/projects/markdown/syntax) at Daring Fireball.

If you prefer to learn by example, see the following source and result:

  * [Source](sample_content.html)
  * [Result](http://github.com/mojombo/github-flavored-markdown/issues/#issue/1)

If you're interested in how we render Markdown files, you might want to check out [Redcarpet](https://github.com/vmg/redcarpet), our Ruby interface to the [Sundown](https://www.github.com/vmg/sundown) library.

## Differences from traditional Markdown

### Newlines

The biggest difference that GFM introduces is in the handling of linebreaks.  With SM you can hard wrap paragraphs of text and they will be combined into a single paragraph.  We find this to be the cause of a huge number of unintentional formatting errors.  GFM treats newlines in paragraph-like content as real line breaks, which is probably what you intended.

The next paragraph contains two phrases separated by a single newline character:

    Roses are red
    Violets are blue

becomes

Roses are red
Violets are blue

### Multiple underscores in words

It is not reasonable to italicize just _part_ of a word, especially when you're dealing with code and names often appear with multiple underscores.  Therefore, GFM ignores multiple underscores in words.

    perform_complicated_task
    do_this_and_do_that_and_another_thing

becomes

perform_complicated_task do_this_and_do_that_and_another_thing

### URL autolinking

GFM will autolink standard URLs, so if you want to link to a URL (instead of setting link text), you can simply enter the URL and it will be turned into a link to that URL.

### Fenced code blocks

Markdown converts text with four spaces at the front of each line to code blocks.  GFM supports that, but we also support fenced blocks.  Just wrap your code blocks in `` ``` `` and you won't need to indent manually to trigger a code block.

### Syntax highlighting

We take code blocks a step further and add syntax highlighting if you request
it. In your fenced block, add an optional language identifier and we'll run it
through syntax highlighting. For example, to syntax highlight Ruby code:

    ```ruby
    require 'redcarpet'
    markdown = Redcarpet.new("Hello World!")
    puts markdown.to_html
    ```

This yields

```ruby
require 'redcarpet'
markdown = Redcarpet.new("Hello World!")
puts markdown.to_html
```

## Code

The newline and underscore modification code can be seen below.  If you find a bug in the rendering, we'd love to hear about it.  Browse through open Issues and report new Issues on the [GitHub-flavored Markdown Issues page](https://github.com/github/github-flavored-markdown/issues).

## Markdown Cheat Sheet

On Markdown-enabled portions of the site, press **M** on your keyboard to display a cheat sheet.

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<http://github.github.com/github-flavored-markdown/>
