@MaximeKjaer Sorry that it's taken so long to get back to you on this. I'm going through the lexers and will have some comments soon!

Sorry, there's a lot there! Please don't hesitate to post any questions you might have! Or any corrections to silly things I said :)

Thank you so much for this extensive review 🎉 I'm happy to have learned a bunch while working on this, it's been fun :)

I've replied to all your points individually above. As I said in one of the replies, I rebased to make sure all code examples throughout the commit history are from a permissive copyright license, and used with the appropriate copyright notice.

Rebasing messed a little bit with the displayed ordering of commits on GitHub. so I'm sorry about that 😬 Apparently this is only a GitHub-specific issue; the commits are fine, and are in the correct order -- it's just GitHub displaying them incorrectly on the PR UI. As the help page says:

If you always want to see commits in order, we recommend not using git rebase. However, rest assured that nothing is broken when you see things outside of a chronological order!

@MaximeKjaer In order to reduce warnings issued from the Ruby interpreter, we recommend using the %r syntax for regular expression literals passed as arguments (e.g. to the method :rule). (However, optionally using that syntax everywhere brings consistency).

Also, it'd be better if individual method definitions are separated by a blank line:

      # Terminal literals:
      # https://www.w3.org/TR/xpath-31/#terminal-symbols

      def self.digits
        @digits ||= %r/[0-9]+/
      end

      def self.decimalLiteral
        @decimalLiteral ||= %r/\.#{digits}|#{digits}\.[0-9]*/
      end

      def self.doubleLiteral
        @doubleLiteral ||= %r/(\.#{digits})|#{digits}(\.[0-9]*)?[eE][+-]?#{digits}/
      end

      # Operators
      rule XPath.operators, Operator
      rule %r/\b#{XPath.word_operators}\b/, Operator::Word
      rule %r/\b#{XPath.keywords}\b/, Keyword
      rule %r/[?,{}()\[\]]/, Punctuation

      # Functions
      rule %r/(function)(\s*)(#{XPath.openParen})/ do # function declaration
        groups Keyword, Text::Whitespace, Punctuation
      end

For further details and examples, you may refer to #1180

@ashmaroli Thank you for the feedback! Spacing is fixed in 64f0276, and %r in 96f2614

The code review is a lot of work to, so thank you!

I've addressed all your comments individually, and added an XPath spec in c5ceb2c.

@MaximeKjaer Thanks for doing such a massive amount of work and for being so responsive to all our suggestions. Rouge is a better library as a result of this PR :)

Awesome, thank you all! Hope GitHub updates to this version of Rouge soon.

@zyv My understanding is that GitHub has its own proprietary syntax highlighting library for the code displayed on GitHub proper. With GitHub Pages, GitHub does use Rouge but it's unfortunately a very old version. I'm hoping they update that soon :(

Hope they update the version soon. I wrote the Support and in their Forum. Would be of utmost importance for me.