/usr/share/javascript/prettify/lang-r.js is in libjs-prettify 2013.03.04+dfsg-4.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 | PR.registerLangHandler(PR.createSimpleLexer([["pln",/^[\t\n\r \xA0]+/,null,"\t\n\r \u00a0"],["str",/^\"(?:[^\"\\]|\\[\s\S])*(?:\"|$)/,null,'"'],["str",/^\'(?:[^\'\\]|\\[\s\S])*(?:\'|$)/,null,"'"]],[["com",/^#.*/],["kwd",/^(?:if|else|for|while|repeat|in|next|break|return|switch|function)(?![A-Za-z0-9_.])/],["lit",/^0[xX][a-fA-F0-9]+([pP][0-9]+)?[Li]?/],["lit",/^[+-]?([0-9]+(\.[0-9]+)?|\.[0-9]+)([eE][+-]?[0-9]+)?[Li]?/],["lit",/^(?:NULL|NA(?:_(?:integer|real|complex|character)_)?|Inf|TRUE|FALSE|NaN|\.\.(?:\.|[0-9]+))(?![A-Za-z0-9_.])/],
["pun",/^(?:<<?-|->>?|-|==|<=|>=|<|>|&&?|!=|\|\|?|\*|\+|\^|\/|!|%.*?%|=|~|\$|@|:{1,3}|[\[\](){};,?])/],["pln",/^(?:[A-Za-z]+[A-Za-z0-9_.]*|\.[a-zA-Z_][0-9a-zA-Z\._]*)(?![A-Za-z0-9_.])/],["str",/^`.+`/]]),["r","s","R","S","Splus"]);
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