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The code we use to render README.your_favorite_markup

GitHub Markup

We use this library on GitHub when rendering your README or any other rich text file. The generated HTML is then run through filters in the html-pipeline to perform things like sanitization and syntax highlighting.


The following markups are supported. The dependencies listed are required if you wish to run the library. You can also run script/bootstrap to fetch them all.


gem install github-markup


require 'github/markup'
GitHub::Markup.render('README.markdown', "* One\n* Two")

Or, more realistically:

require 'github/markup'


See Contributing

HTML sanitization

HTML rendered by the various markup language processors gets passed through an HTML sanitization filter for security reasons. HTML elements not in the whitelist are removed. HTML attributes not in the whitelist are removed from the preserved elements.

The following HTML elements, organized by category, are whitelisted:

Type Elements
Headings h1, h2, h3, h4, h5, h6, h7, h8
Prose p, div, blockquote
Formatted pre
Inline b, i, strong, em, tt, code, ins, del, sup, sub, kbd, samp, q, var
Lists ol, ul, li, dl, dt, dd
Tables table, thead, tbody, tfoot, tr, td, th
Breaks br, hr
Ruby (East Asian) ruby, rt, rp

The following attributes, organized by element, are whitelisted:

Element Attributes
a href (http://, https://, mailto://, github-windows://, and github-mac:// URI schemes and relative paths only)
img src (http:// and https:// URI schemes and relative paths only)
div itemscope, itemtype
All abbr, accept, accept-charset, accesskey, action, align, alt, axis, border, cellpadding, cellspacing, char, charoff, charset, checked, cite, clear, cols, colspan, color, compact, coords, datetime, dir, disabled, enctype, for, frame, headers, height, hreflang, hspace, ismap, label, lang, longdesc, maxlength, media, method, multiple, name, nohref, noshade, nowrap, prompt, readonly, rel, rev, rows, rowspan, rules, scope, selected, shape, size, span, start, summary, tabindex, target, title, type, usemap, valign, value, vspace, width, itemprop

Note that the id attribute is not whitelisted.

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