diff --git a/pythonx/UltiSnips/buffer_helper.py b/pythonx/UltiSnips/buffer_proxy.py
similarity index 64%
rename from pythonx/UltiSnips/buffer_helper.py
rename to pythonx/UltiSnips/buffer_proxy.py
index 40366d1..312f258 100644
--- a/pythonx/UltiSnips/buffer_helper.py
+++ b/pythonx/UltiSnips/buffer_proxy.py
@@ -9,8 +9,13 @@ from UltiSnips import _vim
 
 from contextlib import contextmanager
 
+
 @contextmanager
 def use_proxy_buffer(snippets_stack):
+    """
+    Forward all changes made in the buffer to the current snippet stack while
+    function call.
+    """
     buffer_proxy = VimBufferProxy(snippets_stack)
     old_buffer = _vim.buf
     try:
@@ -20,8 +25,12 @@ def use_proxy_buffer(snippets_stack):
         _vim.buf = old_buffer
     buffer_proxy.validate_buffer()
 
+
 @contextmanager
 def suspend_proxy_edits():
+    """
+    Prevents changes being applied to the snippet stack while function call.
+    """
     if not isinstance(_vim.buf, VimBufferProxy):
         yield
     else:
@@ -31,17 +40,47 @@ def suspend_proxy_edits():
         finally:
             _vim.buf._enable_edits()
 
+
 class VimBufferProxy(_vim.VimBuffer):
+    """
+    Proxy object used for tracking changes that made from snippet actions.
+
+    Unfortunately, vim by itself lacks of the API for changing text in
+    trackable maner.
+
+    Vim marks offers limited functionality for tracking line additions and
+    deletions, but nothing offered for tracking changes withing single line.
+
+    Instance of this class is passed to all snippet actions and behaves as
+    internal vim.current.window.buffer.
+
+    All changes that are made by user passed to diff algorithm, and resulting
+    diff applied to internal snippet structures to ensure they are in sync with
+    actual buffer contents.
+    """
+
     def __init__(self, snippets_stack):
+        """
+        Instantiate new object.
+
+        snippets_stack is a slice of currently active snippets.
+        """
         self._snippets_stack = snippets_stack
         self._buffer = vim.current.buffer
         self._change_tick = int(vim.eval("b:changedtick"))
         self._forward_edits = True
 
     def is_buffer_changed_outside(self):
+        """
+        Returns true, if buffer was changed without using proxy object, like
+        with vim.command() or through internal vim.current.window.buffer.
+        """
         return self._change_tick < int(vim.eval("b:changedtick"))
 
     def validate_buffer(self):
+        """
+        Raises exception if buffer is changes beyound proxy object.
+        """
         if self.is_buffer_changed_outside():
             raise RuntimeError('buffer was modified using vim.command or ' +
             'vim.current.buffer; that changes are untrackable and leads to ' +
@@ -49,6 +88,10 @@ class VimBufferProxy(_vim.VimBuffer):
             'for buffer modifications')
 
     def __setitem__(self, key, value):
+        """
+        Behaves as vim.current.window.buffer.__setitem__ except it tracks
+        changes and applies them to the current snippet stack.
+        """
         if isinstance(key, slice):
             value = [as_vimencoding(l) for l in value]
             changes = list(self._get_diff(key.start, key.stop, value))
@@ -65,21 +108,36 @@ class VimBufferProxy(_vim.VimBuffer):
                 self._apply_change(change)
 
     def __setslice__(self, i, j, text):
+        """
+        Same as __setitem__.
+        """
         self.__setitem__(slice(i, j), text)
 
     def __getitem__(self, key):
+        """
+        Just passing call to the vim.current.window.buffer.__getitem__.
+        """
         if isinstance(key, slice):
             return [as_unicode(l) for l in self._buffer[key.start:key.stop]]
         else:
             return as_unicode(self._buffer[key])
 
     def __getslice__(self, i, j):
+        """
+        Same as __getitem__.
+        """
         return self.__getitem__(slice(i, j))
 
     def __len__(self):
+        """
+        Same as len(vim.current.window.buffer).
+        """
         return len(self._buffer)
 
     def append(self, line, line_number=-1):
+        """
+        Same as vim.current.window.buffer.append(), but with tracking changes.
+        """
         if line_number < 0:
             line_number = len(self)
         if not isinstance(line, list):
@@ -93,6 +151,9 @@ class VimBufferProxy(_vim.VimBuffer):
             self.__setitem__(slice(key, key+1), [])
 
     def _get_diff(self, start, end, new_value):
+        """
+        Very fast diffing algorithm when changes are across many lines.
+        """
         for line_number in range(start, end):
             yield ('D', line_number, 0, self._buffer[line_number])
 
@@ -100,6 +161,9 @@ class VimBufferProxy(_vim.VimBuffer):
             yield ('I', start+line_number, 0, new_value[line_number])
 
     def _get_line_diff(self, line_number, before, after):
+        """
+        Use precise diffing for tracking changes in single line.
+        """
         if before == '':
             for change in self._get_diff(line_number, line_number+1, [after]):
                 yield change
@@ -108,6 +172,10 @@ class VimBufferProxy(_vim.VimBuffer):
                 yield (change[0], line_number, change[2], change[3])
 
     def _apply_change(self, change):
+        """
+        Apply changeset to current snippets stack, correctly moving around
+        snippet itself or its child.
+        """
         if not self._snippets_stack:
             return
 
@@ -128,7 +196,15 @@ class VimBufferProxy(_vim.VimBuffer):
             self._snippets_stack[0]._do_edit(change)
 
     def _disable_edits(self):
+        """
+        Temporary disable applying changes to snippets stack. Should be done
+        while expanding anonymous snippet in the middle of jump to prevent
+        double tracking.
+        """
         self._forward_edits = False
 
     def _enable_edits(self):
+        """
+        Enables changes forwarding back.
+        """
         self._forward_edits = True