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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 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'

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:

  • Headings: h1, h2, h3, h4, h5, h6, h7, h8
  • Prose: p, div, blockquote
  • Preformatted: 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:

  • 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.


See Contributing

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