Added unicode chapter to the docs. This fixes #67

docs/contents.rst.inc

@@ -42,6 +42,7 @@ Design notes, legal information and changelog are here for the interested.
    design
    htmlfaq
    security
+   unicode
    extensiondev
    license
    upgrading

docs/unicode.rst

@@ -0,0 +1,81 @@
+Unicode in Flask
+================
+
+Flask like Jinja2 and Werkzeug is totally unicode based when it comes to
+text.  Not only these libraries, also the majority of web related Python
+libraries that deal with text.  If you don't know unicode so far, you
+should probably read `The Absolute Minimum Every Software Developer
+Absolutely, Positively Must Know About Unicode and Character Sets
+<http://www.joelonsoftware.com/articles/Unicode.html>`_.  This part of the
+documentation just tries to cover the very basics so that you have a
+pleasent experience with unicode related things.
+
+Automatic Conversion
+--------------------
+
+Flask has a few assumptions about your application (which you can change
+of course) that give you basic and painless unicode support:
+
+-   the encoding for text on your website is UTF-8
+-   internally you will always use unicode exclusively for text except
+    for literal strings with only ASCII character points.
+-   encoding and decoding happens whenever you are talking over a protocol
+    that requires bytes to be transmitted.
+
+So what does this mean to you?
+
+HTTP is based on bytes.  Not only the protocol, also the system used to
+address documents on servers (so called URIs or URLs).  However HTML which
+is usually transmitted on top of HTTP supports a large variety of
+character sets and which ones are used, are transmitted in an HTTP header.
+To not make this too complex Flask just assumes that if you are sending
+unicode out you want it to be UTF-8 encoded.  Flask will do the encoding
+and setting of the appropriate headers for you.
+
+The same is true if you are talking to databases with the help of
+SQLAlchemy or a similar ORM system.  Some databases have a protocol that
+already transmits unicode and if they do not, SQLAlchemy or your other ORM
+should take care of that.
+
+The Golden Rule
+---------------
+
+So the rule of thumb: if you are not dealing with binary data, work with
+unicode.  What does working with unicode in Python 2.x mean?
+
+-   as long as you are using ASCII charpoints only (basically numbers,
+    some special characters of latin letters without umlauts or anything
+    fancy) you can use regular string literals (``'Hello World'``).
+-   if you need anything else than ASCII in a string you have to mark
+    this string as unicode string by prefixing it with a lowercase `u`.
+    (like ``u'Hänsel und Gretel'``)
+-   if you are using non-unicode characters in your Python files you have
+    to tell Python which encoding your file uses.  Again, I recommend
+    UTF-8 for this purpose.  To tell the interpreter yuor encoding you can
+    put the ``# -*- coding: utf-8 -*-`` into the first or second line of
+    your Python source file.
+
+Encoding and Decoding Yourself
+------------------------------
+
+If you are talking with a filesystem or something that is not really based
+on unicode you will have to ensure that you decode properly when working
+with unicode interface.  So for example if you want to load a file on the
+filesystem and embedd it into a Jinja2 template you will have to decode it
+form the encoding of that file.  Here the old problem that textfiles do
+not specify their encoding comes into play.  So do yourself a favour and
+limit yourself to UTF-8 for textfiles as well.
+
+Anyways.  To load such a file with unicode you can use the builtin
+:meth:`str.decode` method::
+
+    def read_file(filename, charset='utf-8'):
+        with open(filename, 'r') as f:
+            return f.read().decode(charset)
+
+To go from unicode into a specific charset such as UTF-8 you can use the
+:meth:`unicode.encode` method::
+
+    def write_file(filename, contents, charset='utf-8'):
+        with open(filename, 'w') as f:
+            f.write(contents.encode(charset))