diff --git a/NOTES.md b/NOTES.md
new file mode 100644
index 0000000..237ca0a
--- /dev/null
+++ b/NOTES.md
@@ -0,0 +1,7 @@
+Workflow for releasing a new version:
+
+1. Update the version in `setup.py` (even the `download_url`). Commit it with message "Bump version to x.x.x"
+2. Tag the new commit as vx.x.x (v1.1, v1.0.1)
+3. Push to Github
+4. Update the releases page: https://github.com/BoGoEngine/bogo-python/releases
+5. Upload to PyPI: https://docs.python.org/2/distutils/packageindex.html#package-index
\ No newline at end of file
diff --git a/README.md b/README.md
index a2d835e..2ee3e5a 100644
--- a/README.md
+++ b/README.md
@@ -4,8 +4,7 @@ BoGo
 [![Build Status](https://travis-ci.org/BoGoEngine/bogo-python.svg?branch=master)](https://travis-ci.org/BoGoEngine/bogo-python)
 [![Coverage Status](https://coveralls.io/repos/BoGoEngine/bogo-python/badge.png?branch=master)](https://coveralls.io/r/BoGoEngine/bogo-python?branch=master)
 
-BoGo is a Vietnamese input method conversion library for Python. This library
-is intentionally functional with no internal state and side-effect.
+BoGo is a Vietnamese input method conversion library for Python.
 
 Installation
 ------------
@@ -43,3 +42,8 @@ Some functions from `bogo.core` are exported to package toplevel:
 - `get_vni_definition()`
 
 BoGo is extensively tested with Python 2.7, Python 3.2 and Python 3.3.
+
+Etymology
+---------
+
+BoGo, or more precisely *bộ gõ*, literally means *input method* in Vietnamese.
diff --git a/bogo/__init__.py b/bogo/__init__.py
index d507d7c..a147ff5 100644
--- a/bogo/__init__.py
+++ b/bogo/__init__.py
@@ -28,4 +28,5 @@
     process_key, \
     process_sequence, \
     get_telex_definition, \
-    get_vni_definition
+    get_vni_definition, \
+    handle_backspace
diff --git a/bogo/core.py b/bogo/core.py
index 697e3ba..8e16783 100644
--- a/bogo/core.py
+++ b/bogo/core.py
@@ -101,16 +101,14 @@ def get_vni_definition():
 
 def _accepted_chars(rules):
     if sys.version_info[0] > 2:
-        accepted_chars = \
-            string.ascii_letters + \
-            ''.join(rules.keys())
+        ascii_letters = \
+            string.ascii_letters
     else:
-        accepted_chars = \
+        ascii_letters = \
             string.lowercase + \
-            string.uppercase + \
-            ''.join(rules.keys())
+            string.uppercase
 
-    return accepted_chars
+    return set(ascii_letters + ''.join(rules.keys()) + utils.VOWELS + "đ")
 
 
 def process_sequence(sequence,
@@ -489,3 +487,59 @@ def atomic_check(action):
                     accent.remove_accent_char(comps[1][-1]))  # ơ, ư
 
     return any(map(atomic_check, action_list))
+
+
+def handle_backspace(converted_string, raw_sequence, im_rules=None):
+    """
+    Returns a new raw_sequence after a backspace. This raw_sequence should
+    be pushed back to process_sequence().
+    """
+    # I can't find a simple explanation for this, so
+    # I hope this example can help clarify it:
+    #
+    # handle_backspace(thương, thuwongw) -> thuwonw
+    # handle_backspace(thươn, thuwonw) -> thuwow
+    # handle_backspace(thươ, thuwow) -> thuw
+    # handle_backspace(thươ, thuw) -> th
+    #
+    # The algorithm for handle_backspace was contributed by @hainp.
+
+    if im_rules == None:
+        im_rules = get_telex_definition()
+
+    deleted_char = converted_string[-1]
+
+    _accent = accent.get_accent_char(deleted_char)
+    _mark = mark.get_mark_char(deleted_char)
+
+    if _mark or _accent:
+        # Find a sequence of IM keys at the end of
+        # raw_sequence
+
+        ime_keys_at_end = ""
+        len_raw_sequence = len(raw_sequence)
+        i = len_raw_sequence - 1
+
+        while i >= 0:
+            if raw_sequence[i] not in im_rules and \
+                    raw_sequence[i] not in "aeiouyd":
+                i += 1
+                break
+            else:
+                ime_keys_at_end = raw_sequence[i] + ime_keys_at_end
+            i -= 1
+
+        # Try to find a subsequence from that sequence
+        # that can be converted to the deleted_char
+        k = 0
+        while k < len_raw_sequence:
+            if process_sequence(raw_sequence[i + k:], im_rules) == deleted_char:
+                # Delete that subsequence
+                raw_sequence = raw_sequence[:i + k]
+                break
+            k += 1
+    else:
+        index = raw_sequence.rfind(deleted_char)
+        raw_sequence = raw_sequence[:index] + raw_sequence[(index + 1):]
+
+    return raw_sequence
diff --git a/bogo/test/test_engine.py b/bogo/test/test_engine.py
index 35b871f..db1fa70 100644
--- a/bogo/test/test_engine.py
+++ b/bogo/test/test_engine.py
@@ -6,7 +6,8 @@
 from functools import partial
 import codecs
 
-from bogo.core import _Action, _get_action, process_sequence
+import bogo
+from bogo.core import _Action, _get_action, process_sequence, handle_backspace
 from bogo.mark import Mark
 import os
 
@@ -189,3 +190,39 @@ def test_with_separator(self):
         eq_(process_sequence('con meof dideen'), 'con mèo điên')
         eq_(process_sequence('con.meof'), 'con.mèo')
         eq_(process_sequence('con?meof'), 'con?mèo')
+
+    def test_change_tone(self):
+        eq_(process_sequence('meofs'), 'méo')
+        eq_(process_sequence('mèos'), 'méo')
+
+
+class TestHandleBackspace():
+
+    def test_delete_non_im_key(self):
+        eq_(handle_backspace('an', 'an'), 'a')
+        eq_(handle_backspace('a', 'a'), '')
+
+    def test_delete_one_im_key(self):
+        eq_(handle_backspace('bà', 'baf'), 'b')
+        eq_(handle_backspace('bâ', 'baa'), 'b')
+        eq_(handle_backspace('sý', 'sys'), 's')
+
+    def test_delete_two_im_keys(self):
+        eq_(handle_backspace('bớ', 'bows'), 'b')
+    
+    def test_non_im_key_before_im_key(self):
+        eq_(handle_backspace('bân', 'bana'), 'baa')
+
+    def test_im_insert_key(self):
+        eq_(handle_backspace('bư', 'bw'), 'b')
+        eq_(handle_backspace('boư', 'bow'), 'bo')
+        eq_(handle_backspace('bá', 'bafjxrs'), 'b')
+        eq_(handle_backspace('bá', 'ba23451',
+            bogo.core.get_vni_definition()), 'b')
+
+        # FIXME
+        # eq_(handle_backspace('dườ', 'duwfow'), 'duw')
+        # eq_(handle_backspace('uyể', 'uryee'), 'uy')
+
+    def test_single_im_key_two_vowels(self):
+        eq_(handle_backspace('bươ', 'buow'), 'bu')
\ No newline at end of file
diff --git a/setup.py b/setup.py
index c55104a..e1d04c2 100644
--- a/setup.py
+++ b/setup.py
@@ -5,12 +5,12 @@
 setup(
     name='bogo',
     packages=['bogo'],
-    version='1.0.1',
+    version='1.1',
     description='Library for implementing Vietnamese input method editors with a purely functional interface.',
     author='Trung Ngo',
     author_email='ndtrung4419@gmail.com',
     url='https://github.com/BoGoEngine/bogo-python',
-    download_url='https://github.com/BoGoEngine/bogo-python/archive/v1.0.tar.gz',
+    download_url='https://github.com/BoGoEngine/bogo-python/archive/v1.1.tar.gz',
     keywords=['vietnamese'],
     classifiers=[
         "Programming Language :: Python",