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 = []