diff --git a/src/diana/diana.py b/src/diana/diana.py
--- a/src/diana/diana.py
+++ b/src/diana/diana.py
@@ -11,6 +11,11 @@ from .drawer.tikz import Tikz
 
 
 def collect_moves(root):
+	"""Walk the primary variation and collect the move coordinates.
+
+	:param Node root: a node serving as a root for the tree traversal
+	:return: sequence of move colors and coordinates (col, row)
+	:rtype: Iterator[("b" or "w", (int, int))]"""
 	node = root
 	while len(node.children) > 0:
 		b = node.get_prop("B")
@@ -55,6 +60,13 @@ W: {PW} {WR}
 		print("done")
 
 	def create_diagram(self, start, end):
+		"""Create and return a diagram drawer instance.
+
+		:param int start: the initial move
+		:param int end: the first omitted move, similar to sequence slices
+		:return: a diagram instance
+		:rtype: Drawer"""
+
 		# initialize the diagram
 		template = Svg()
 
@@ -73,7 +85,7 @@ W: {PW} {WR}
 
 			color, move = self._moves[k]
 			if move == tuple():
-				template.overlays.append((k, "pass"))  # !!
+				template.overlays.append((k, "pass"))
 				continue
 			else:
 				(c, r) = move
@@ -93,6 +105,9 @@ W: {PW} {WR}
 		return {k: self._record.get(k, default) for k in field_names}
 
 	def _set_move(self, k):
+		"""Rewind the internal game state to move k.
+
+		:param int k: the move number"""
 		self._game = go.Go()
 
 		black_stones = self._record.root.get_prop("AB")
@@ -107,13 +122,20 @@ W: {PW} {WR}
 		for i in range(k):
 			(color, move) = self._moves[i]
 			if move == tuple():
-				continue # pass
+				continue  # pass
 			self._move(color, *move)
 
 	def _move(self, color, c, r):
+		"""Make a single move.
+
+		:param str color: "b" or "w"
+		:param int c: column
+		:param int r: row
+		:return: True if we can continue with another move, False on abort"""
 		if not self._game.move(BLACK if color=='b' else WHITE, c, r):
-			# !! we do not honor http://red-bean.com/sgf/ff5/m_vs_ax.htm at the moment
-			msg = "illegal move: {0} at {1},{2}".format(self._game.move_count + 1, c, r)
+			# we do not honor http://red-bean.com/sgf/ff5/m_vs_ax.htm at the moment
+			# we accept and process only legal moves
+			msg = "illegal move: {0} at {1},{2}".format(self._game.move_count+1, c, r)
 			if cfg.keep_broken:
 				print(msg)
 			else:
diff --git a/src/diana/drawer/svg.py b/src/diana/drawer/svg.py
--- a/src/diana/drawer/svg.py
+++ b/src/diana/drawer/svg.py
@@ -23,6 +23,12 @@ class Svg(Drawer):
 		self.padding = 30
 
 	def render(self, template_name, bgcolor=""):
+		"""Render the template with the current drawer state.
+
+		:param str template_name: a template file name in the templ directory
+		:param bgcolor: a background color
+		:type bgcolor: an SVG color, which is the same as a CSS color
+		:return: the rendered template string"""
 		points = [p for (i, p) in sorted(self._index.values(), key=lambda x: x[0])]
 
 		stones = [p for p in points if p.color and p.label == ""]
@@ -36,6 +42,12 @@ class Svg(Drawer):
 		return self._env.get_template(template_name).render(params)
 
 	def save(self, filename, template="templ.svg", bgcolor=""):
+		"""Render the template and save it with the filename.
+
+		:param str filename: a path where to save the diagram. SVG and TXT suffixes will be appended
+		:param str template: a template file name in the templ directory
+		:param bgcolor: a background color
+		:type bgcolor: an SVG color, which is the same as a CSS color"""
 		file = open(filename+".svg", 'w')
 		file.write(self.render(template, bgcolor))
 		file.close()
diff --git a/src/diana/go.py b/src/diana/go.py
--- a/src/diana/go.py
+++ b/src/diana/go.py
@@ -12,6 +12,12 @@ class Go:
 		self.temp = [[]]
 	
 	def move(self, color, y, x):
+		"""Update the board with the specified move.
+
+		:param int color: BLACK or WHITE
+		:param int y: the row number
+		:param int x: the column number
+		:return: True on success, False on an invalid move"""
 		if self.board[x][y] != EMPTY:
 			return False
 
@@ -39,10 +45,10 @@ class Go:
 			return False
 		self.temp[x][y] = True
 
-		return self._flood_fill(color, x - 1, y) or \
-			self._flood_fill(color, x + 1, y) or \
-			self._flood_fill(color, x, y - 1) or \
-			self._flood_fill(color, x, y + 1)
+		return self._flood_fill(color, x-1, y) or \
+			self._flood_fill(color, x+1, y) or \
+			self._flood_fill(color, x, y-1) or \
+			self._flood_fill(color, x, y+1)
 	
 	def _remove(self):
 		for i in range(19):
diff --git a/src/diana/sgfparser/__init__.py b/src/diana/sgfparser/__init__.py
--- a/src/diana/sgfparser/__init__.py
+++ b/src/diana/sgfparser/__init__.py
@@ -1,4 +1,9 @@
 def skip_whitespace(s, start):
+	"""Find the first non-whitespace character in a string.
+
+	:param str s: an input string
+	:param int start: an index where the search starts
+	:return: index of the first non-whitespace character or len(s)"""
 	i = start
 	while i < len(s) and s[i].isspace():
 		i += 1
@@ -7,6 +12,12 @@ def skip_whitespace(s, start):
 
 
 def str_row_col(s, i):
+	"""Translate a string index i to a row and col number.
+
+	:param str s: an input string
+	:param int i: an index pointing into s
+	:return: a string position as (row, col)
+	:rtype: (int, int)"""
 	k = 0
 	(r, c) = (0, 0)
 	for (r, line) in enumerate(s.splitlines(True)):
diff --git a/src/diana/sgfparser/collection.py b/src/diana/sgfparser/collection.py
--- a/src/diana/sgfparser/collection.py
+++ b/src/diana/sgfparser/collection.py
@@ -4,6 +4,8 @@ from .game_record import GameRecord
 
 
 class Collection:
+	"""Game collection type, a list of game trees."""
+
 	def __init__(self, s):
 		self.game_trees = []
 		i = skip_whitespace(s, 0)
@@ -18,6 +20,7 @@ class Collection:
 			raise ParserError("expected EOF", s, i)
 
 	def list_games(self):
+		""":rtype: Iterator[GameRecord]"""
 		for tree in self.game_trees:
 			for game in tree.list_games():
 				yield game
@@ -30,10 +33,21 @@ class GameTree:
 
 	@staticmethod
 	def fits(s, i):
+		"""Decide if a GameTree fits at the suggested string location.
+
+		:param str s: an SGF string
+		:param int i: a string location
+		:return: True if there might be a GameTree at the location, False if not"""
 		return i < len(s) and s[i] == "("
 
 	@staticmethod
 	def create(s, start):
+		"""Create a GameTree from the string and move the current position pointer.
+
+		:param str s: an SGF string
+		:param int start: a location in s
+		:return: the resulting tree and a pointer to its end
+		:rtype: (int, GameTree)"""
 		assert GameTree.fits(s, start)
 		res = GameTree()
 
@@ -65,8 +79,8 @@ class GameTree:
 		i = skip_whitespace(s, i + 1)
 		return (i, res)
 
-	## Expand multiple games into distinct GameTrees and yield each.
 	def list_games(self):
+		"""Expand multiple games into distinct GameTrees and yield each."""
 		if len(self.nodes) == 0:
 			return None
 		for node in self.nodes[0].list_gi_nodes():
@@ -77,10 +91,10 @@ class GameTree:
 			return self.nodes[i]
 		return None
 
-	## Create and return a new game tree containing the provided Node.
-	#
-	# Ancestor nodes are copied, descendants are moved from the seed_node.
 	def _build_subtree(self, seed_node):
+		"""Create and return a new game tree containing the provided Node.
+
+		Ancestor nodes are copied, descendants are moved from the seed_node."""
 		node = seed_node.copy()
 		node.set_children(seed_node.children)
 		seed_node.children = []
diff --git a/src/diana/sgfparser/game_record.py b/src/diana/sgfparser/game_record.py
--- a/src/diana/sgfparser/game_record.py
+++ b/src/diana/sgfparser/game_record.py
@@ -1,8 +1,9 @@
 from .node import Node
 
 
-## Wrapper around a Node tree.
 class GameRecord:
+	"""Wrapper around a Node tree."""
+
 	def __init__(self, root=None):
 		self.root = root or Node()
 		self._game_info_node = next(root.list_gi_nodes())
diff --git a/src/diana/sgfparser/node.py b/src/diana/sgfparser/node.py
--- a/src/diana/sgfparser/node.py
+++ b/src/diana/sgfparser/node.py
@@ -86,8 +86,8 @@ class Node:
 			return res
 		return None
 
-	## Create a copy of the Node, with the same parent and deep copied properties, no copied children.
 	def copy(self):
+		"""Create a copy of the Node, with the same parent and deep copied properties, no copied children."""
 		res = Node()
 		res.properties = {k: v.copy() for (k, v) in self.properties.items()}
 		res.parent = self.parent
@@ -99,8 +99,8 @@ class Node:
 		else:
 			return default
 
-	## Returns textual representation of the Node itself, but disregards its children.
 	def __str__(self):
+		"""Returns textual representation of the Node itself, but disregards its children."""
 		return ";" + "".join(str(p) for p in self.properties.values())
 
 	def export(self):