[kayodelycaon]

Rails has had Builder::XmlMarkup for a long time. It's been extracted into a gem: https://www.rubydoc.info/gems/builder/Builder/XmlMarkup

You could easily write a method to do this:

    def html(&blk)
      io = StringIO.new()
      builder = Builder::XmlMarkup.new(:target => io, :indent => 2)
      blk.call(builder)
      io.to_s
    end

    html do |t|
      t.span "#{@first_name} #{@last_name}"
    end

Not the prettiest, but it doesn't require additional gems or a new syntax highlighter and linter.

[ImaCake]

Surely rux would cover more edge cases than your function? A lot of people would see this function and struggle to understand what it is doing, but if you explicitly use something like rux it's much more obvious. I guess rux would have more overhead than this though.