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+# Developer README #
+
+This file is intended to provide a place for developers and contributors to
+document what other developers need to know about changes made to Puppet.
+
+# UTF-8 Handling #
+
+As Ruby 1.9 becomes more commonly used with Puppet, developers should be aware
+of major changes to the way Strings and Regexp objects are handled.
+Specifically, every instance of these two classes will have an encoding
+attribute determined in a number of ways.
+
+ * If the source file has an encoding specified in the magic comment at the
+   top, the instance will take on that encoding.
+ * Otherwise, the encoding will be determined by the LC\_LANG or LANG
+   environment variables.
+ * Otherwise, the encoding will default to ASCII-8BIT
+
+## References ##
+
+Excellent information about the differences between encodings in Ruby 1.8 and
+Ruby 1.9 is published in this blog series:
+[Understanding M17n](http://links.puppetlabs.com/understanding_m17n)
+
+## Encodings of Regexp and String instances ##
+
+In general, please be aware that Ruby 1.9 regular expressions need to be
+compatible with the encoding of a string being used to match them.  If they are
+not compatible you can expect to receive and error such as:
+
+    Encoding::CompatibilityError: incompatible encoding regexp match (ASCII-8BIT
+    regexp with UTF-8 string)
+
+In addition, some escape sequences where were valid in Ruby 1.8 are no longer
+valid in 1.9 if the regular expression is not marked as an ASCII-8BIT object.
+You may expect errors like this in this situation:
+
+    SyntaxError: (irb):7: invalid multibyte escape: /\xFF/
+
+This error is particularly comment when serializing a string to other
+representations like JSON or YAML.  To resolve the problem you can explicitly
+mark the regular expression as ASCII-8BIT using the /n flag:
+
+    "a" =~ /\342\230\203/n
+
+Finally, any time you're thinking of a string as an array of bytes rather than
+an array of characters, common when escaping a string, you should work with
+everything in ASCII-8BIT.  Changing the encoding will not change the data
+itself and allow the Regexp and the String to deal with bytes rather than
+characters.
+
+Puppet provides a monkey patch to String which returns an encoding suitable for
+byte manipulations:
+
+    # Example of how to escape non ASCII printable characters for YAML.
+    >> snowman = "☃"
+    >> snowman.to_ascii8bit.gsub(/([\x80-\xFF])/n) { |x| "\\x#{x.unpack("C")[0].to_s(16)} }
+    => "\\xe2\\x98\\x83"
+
+If the Regexp is not marked as ASCII-8BIT using /n, then you can expect the
+SyntaxError, invalid multibyte escape as mentioned above.
+
+EOF