diff --git a/README.rdoc b/README.rdoc
index 5fe0522..deeb716 100644
--- a/README.rdoc
+++ b/README.rdoc
@@ -10,7 +10,7 @@ for any production data yet.
 
 = Demo
 
-  $ ruby examples/demo.rb
+  $ ruby examples/simple.rb
 
 Mongo must be running, of course.
 
diff --git a/lib/mongo/collection.rb b/lib/mongo/collection.rb
index e6c92d4..715aaaa 100644
--- a/lib/mongo/collection.rb
+++ b/lib/mongo/collection.rb
@@ -1,3 +1,4 @@
+# ---
 # Copyright (C) 2008 10gen Inc.
 #
 # This program is free software: you can redistribute it and/or modify it
@@ -11,12 +12,15 @@
 #
 # You should have received a copy of the GNU Affero General Public License
 # along with this program. If not, see <http://www.gnu.org/licenses/>.
+# +++
 
 require 'mongo/query'
 
 module XGen
   module Mongo
     module Driver
+
+      # A named collection of records in a database.
       class Collection
 
         attr_reader :db, :name
@@ -26,18 +30,23 @@ module XGen
           @name = name
         end
 
+        # Return records that match a +selector+ hash. See Mongo docs for
+        # details.
+        #
         # Options:
-        # * <tt>:fields</tt> - Array of collection field names; only those will be returned (plus _id if defined)
-        # * <tt>:offset</tt> - Start at this record when returning records
-        # * <tt>:limit</tt> - Maximum number of records to return
-        # * <tt>:sort</tt> - Hash of field names as keys and 1/-1 as values; 1 == ascending, -1 == descending
-        # <tt>
+        # :fields :: Array of collection field names; only those will be returned (plus _id if defined)
+        # :offset :: Start at this record when returning records
+        # :limit :: Maximum number of records to return
+        # :sort :: Either hash of field names as keys and 1/-1 as values; 1 ==
+        #          ascending, -1 == descending, or array of field names (all
+        #          assumed to be sorted in ascending order).
         def find(selector={}, options={})
           fields = options.delete(:fields)
           fields = nil if fields && fields.empty?
           @db.query(@name, Query.new(selector, fields, options[:offset] || 0, options[:limit] || 0, options[:sort]))
         end
 
+        # Insert +objects+, which are hashes.
         def insert(*objects)
           objects = objects.first if objects.size == 1 && objects.first.is_a?(Array)
           res = @db.insert_into_db(@name, objects)
@@ -45,45 +54,66 @@ module XGen
         end
         alias_method :<<, :insert
 
+        # Remove the records that match +selector+.
         def remove(selector={})
           @db.remove_from_db(@name, selector)
         end
 
+        # Remove all records.
         def clear
           remove({})
         end
 
+        # Update records that match +selector+ by applying +obj+ as an update.
+        # If no match, inserts (???).
         def repsert(selector, obj)
           @db.repsert_in_db(@name, selector, obj)
         end
 
+        # Update records that match +selector+ by applying +obj+ as an update.
         def replace(selector, obj)
           @db.replace_in_db(@name, selector, obj)
         end
 
-        def modify(selector, modifierObj)
-          raise "no object" unless modifierObj
+        # Update records that match +selector+ by applying +obj+ as an update.
+        # Both +selector+ and +modifier_obj+ are required.
+        def modify(selector, modifier_obj)
+          raise "no object" unless modifier_obj
           raise "no selector" unless selector
-          @db.modify_in_db(@name, selector, modifierObj)
+          @db.modify_in_db(@name, selector, modifier_obj)
         end
 
+        # Create a new index named +index_name+. +fields+ should be an array
+        # of field names.
         def create_index(name, *fields)
           @db.create_index(@name, name, fields)
         end
 
+        # Drop index +name+.
         def drop_index(name)
           @db.drop_index(@name, name)
         end
 
+        # Drop all indexes.
         def drop_indexes
           # just need to call drop indexes with no args; will drop them all
           @db.drop_index(@name, '*')
         end
 
+        # Return an array of hashes, one for each index. Each hash contains:
+        #
+        # :name :: Index name
+        #
+        # :keys :: Hash whose keys are the names of the fields that make up
+        #          the key and values are integers.
+        #
+        # :ns :: Namespace; same as this collection's name.
         def index_information
           @db.index_information(@name)
         end
 
+        # Return the number of records that match +selector+. If +selector+ is
+        # +nil+ or an empty hash, returns the count of all records.
         def count(selector={})
           @db.count(@name, selector || {})
         end
diff --git a/lib/mongo/cursor.rb b/lib/mongo/cursor.rb
index 329fb5c..8156c32 100644
--- a/lib/mongo/cursor.rb
+++ b/lib/mongo/cursor.rb
@@ -1,3 +1,4 @@
+# ---
 # Copyright (C) 2008 10gen Inc.
 #
 # This program is free software: you can redistribute it and/or modify it
@@ -11,6 +12,7 @@
 #
 # You should have received a copy of the GNU Affero General Public License
 # along with this program. If not, see <http://www.gnu.org/licenses/>.
+# +++
 
 require 'mongo/message'
 require 'mongo/util/byte_buffer'
@@ -20,6 +22,7 @@ module XGen
   module Mongo
     module Driver
 
+      # A cursor over query results. Returned objects are hashes.
       class Cursor
 
         include Enumerable
@@ -33,10 +36,12 @@ module XGen
           read_all
         end
 
+        # Return +true+ if there are more records to retrieve.
         def more?
           num_remaining > 0
         end
 
+        # Return the next object. Raises an error if necessary.
         def next_object
           refill_via_get_more if num_remaining == 0
           o = @objects.shift
@@ -44,12 +49,14 @@ module XGen
           o
         end
 
+        # Iterate over each object, yielding it to the given block.
         def each
           while more?
             yield next_object()
           end
         end
 
+        # Close the cursor.
         def close
           @db.send_to_db(KillCursorMessage(@cursor_id)) if @cursor_id
           @objects = []
diff --git a/lib/mongo/db.rb b/lib/mongo/db.rb
index 5b8a637..63274b1 100644
--- a/lib/mongo/db.rb
+++ b/lib/mongo/db.rb
@@ -1,3 +1,4 @@
+# ---
 # Copyright (C) 2008 10gen Inc.
 #
 # This program is free software: you can redistribute it and/or modify it
@@ -11,8 +12,10 @@
 #
 # You should have received a copy of the GNU Affero General Public License
 # along with this program. If not, see <http://www.gnu.org/licenses/>.
+# +++
 
 require 'socket'
+require 'mongo/mongo'
 require 'mongo/collection'
 require 'mongo/message'
 require 'mongo/query'
@@ -22,42 +25,64 @@ module XGen
   module Mongo
     module Driver
 
+      # A Mongo database.
       class DB
+
         SYSTEM_NAMESPACE_COLLECTION = "system.namespaces"
         SYSTEM_INDEX_COLLECTION = "system.indexes"
         SYSTEM_COMMAND_COLLECTION = "$cmd"
 
-        # Strict mode means that trying to access a collection that does not
-        # exist will raise an error. Strict mode is off (false) by default.
+        # Strict mode enforces collection existence checks. When +true+,
+        # asking for a collection that does not exist or trying to create a
+        # collection that already exists raises an error.
+        #
+        # Strict mode is off (+false+) by default. Its value can be changed at
+        # any time.
         attr_writer :strict
 
         # Returns the value of the +strict+ flag.
         def strict?; @strict; end
 
-        attr_reader :name, :socket
+        # The name of the database.
+        attr_reader :name
 
-        def initialize(db_name, host, port)
+        # The database's socket. For internal use only.
+        attr_reader :socket
+
+        # db_name :: The database name
+        #
+        # host :: The database host name or IP address. Defaults to 'localhost'.
+        #
+        # port :: The database port number. Defaults to
+        #         XGen::Mongo::Driver::Mongo::DEFAULT_PORT.
+        #
+        def initialize(db_name, host='localhost', port=XGen::Mongo::Driver::Mongo::DEFAULT_PORT)
           raise "Invalid DB name" if !db_name || (db_name && db_name.length > 0 && db_name.include?("."))
           @name, @host, @port = db_name, host, port
           @socket = TCPSocket.new(@host, @port)
           @strict = false
         end
 
+        # Returns an array of collection names. Each name is of the form
+        # "database_name.collection_name".
         def collection_names
           names = collections_info.collect { |doc| doc['name'] || '' }
           names.delete('')
           names
         end
 
+        # Returns a cursor over query result hashes. Each hash contains a
+        # 'name' string and optionally an 'options' hash. If +coll_name+ is
+        # specified, an array of length 1 is returned.
         def collections_info(coll_name=nil)
           selector = {}
-          selector[:name] = "#{@name}.#{coll_name}" if coll_name
+          selector[:name] = full_coll_name(coll_name) if coll_name
           query(SYSTEM_NAMESPACE_COLLECTION, Query.new(selector))
         end
 
         # Create a collection. If +strict+ is false, will return existing or
         # new collection. If +strict+ is true, will raise an error if
-        # collection +name+ does not already exist.
+        # collection +name+ already exists.
         def create_collection(name, options={})
           # First check existence
           if collection_names.include?(full_coll_name(name))
@@ -85,7 +110,17 @@ module XGen
 
         # Return a collection. If +strict+ is false, will return existing or
         # new collection. If +strict+ is true, will raise an error if
-        # collection +name+ already exists.
+        # collection +name+ does not already exists.
+        #
+        # Options:
+        #
+        # :capped :: Boolean. If not specified, capped is +false+.
+        #
+        # :size :: If +capped+ is +true+, specifies the maximum number of
+        #          bytes. If +false+, specifies the initial extent of the
+        #          collection.
+        #
+        # :max :: Max number of records in a capped collection. Optional.
         def collection(name)
           return Collection.new(self, name) if collection_names.include?(full_coll_name(name))
           if strict?
@@ -95,11 +130,13 @@ module XGen
           end
         end
 
+        # Drop collection +name+. Returns +true+ on success or if the
+        # collection does not exist, +false+ otherwise.
         def drop_collection(name)
-          coll = collection(name)
-          return true if coll == nil
-          coll.drop_indexes     # Mongo requires that we drop indexes manually
+          return true unless collection_names.include?(full_coll_name(name))
 
+          coll = collection(name)
+          coll.drop_indexes     # Mongo requires that we drop indexes manually
           ok?(db_command(:drop => name))
         end
 
@@ -111,31 +148,44 @@ module XGen
           ok?(doc) && is_master.kind_of?(Numeric) && is_master.to_i == 1
         end
 
+        # Close the connection to the database.
         def close
           @socket.close
         end
 
+        # Send a MsgMessage to the database.
         def send_message(msg)
           send_to_db(MsgMessage.new(msg))
         end
         
+        # Send a Query to +collection_name+ and return a Cursor over the
+        # results.
         def query(collection_name, query)
           # TODO synchronize
           send_to_db(QueryMessage.new(@name, collection_name, query))
           return Cursor.new(self, collection_name)
         end
 
+        # Remove the records that match +selector+ from +collection_name+.
+        # Normally called by Collection#remove or Collection#clear.
         def remove_from_db(collection_name, selector)
           # TODO synchronize
           send_to_db(RemoveMessage.new(@name, collection_name, selector))
         end
 
+        # Update records in +collection_name+ that match +selector+ by
+        # applying +obj+ as an update. Normally called by Collection#replace.
         def replace_in_db(collection_name, selector, obj)
           # TODO synchronize
           send_to_db(UpdateMessage.new(@name, collection_name, selector, obj, false))
         end
+
+        # Alias for #replace_in_db. Normally called by Collection.modify.
         alias_method :modify_in_db, :replace_in_db
 
+        # Update records in +collection_name+ that match +selector+ by
+        # applying +obj+ as an update. If no match, inserts (???). Normally
+        # called by Collection#repsert.
         def repsert_in_db(collection_name, selector, obj)
           # TODO if PKInjector, inject
           # TODO synchronize
@@ -143,15 +193,20 @@ module XGen
           obj
         end
 
-        def count(collection_name, selector)
+        # Return the number of records in +collection_name+ that match
+        # +selector+. If +selector+ is +nil+ or an empty hash, returns the
+        # count of all records. Normally called by Collection#count.
+        def count(collection_name, selector={})
           oh = OrderedHash.new
           oh[:count] = collection_name
-          oh[:query] = selector
+          oh[:query] = selector || {}
           doc = db_command(oh)
           return doc['n'].to_i if ok?(doc)
           raise "Error with count command: #{doc.inspect}"
         end
 
+        # Drop index +name+ from +collection_name+. Normally called from
+        # Collection#drop_index or Collection#drop_indexes.
         def drop_index(collection_name, name)
           oh = OrderedHash.new
           oh[:deleteIndexes] = collection_name
@@ -160,6 +215,15 @@ module XGen
           raise "Error with drop_index command: #{doc.inspect}" unless ok?(doc)
         end
 
+        # Return an array of hashes, one for each index on +collection_name+.
+        # Normally called by Collection#index_information. Each hash contains:
+        #
+        # :name :: Index name
+        #
+        # :keys :: Hash whose keys are the names of the fields that make up
+        #          the key and values are integers.
+        #
+        # :ns :: Namespace; same as +collection_name+.
         def index_information(collection_name)
           sel = {:ns => full_coll_name(collection_name)}
           # TODO synchronize
@@ -179,6 +243,9 @@ module XGen
           }
         end
 
+        # Create a new index on +collection_name+ named +index_name+. +fields+
+        # should be an array of field names. Normally called by
+        # Collection#create_index.
         def create_index(collection_name, index_name, fields)
           sel = {:name => index_name, :ns => full_coll_name(collection_name)}
           field_h = {}
@@ -188,6 +255,8 @@ module XGen
           send_to_db(InsertMessage.new(@name, SYSTEM_INDEX_COLLECTION, sel))
         end
 
+        # Insert +objects+ into +collection_name+. Normally called by
+        # Collection#insert.
         def insert_into_db(collection_name, objects)
           # TODO synchronize
           objects.each { |o| send_to_db(InsertMessage.new(@name, collection_name, o)) }
@@ -203,6 +272,7 @@ module XGen
 
         protected
 
+        # Return +true+ if +doc+ contains an 'ok' field with the value 1.
         def ok?(doc)
           ok = doc['ok']
           ok.kind_of?(Numeric) && ok.to_i == 1
diff --git a/lib/mongo/mongo.rb b/lib/mongo/mongo.rb
index 773c1b4..654effd 100644
--- a/lib/mongo/mongo.rb
+++ b/lib/mongo/mongo.rb
@@ -1,3 +1,4 @@
+# ---
 # Copyright (C) 2008 10gen Inc.
 #
 # This program is free software: you can redistribute it and/or modify it
@@ -11,6 +12,7 @@
 #
 # You should have received a copy of the GNU Affero General Public License
 # along with this program. If not, see <http://www.gnu.org/licenses/>.
+# +++
 
 require 'mongo/db'
 
@@ -18,22 +20,27 @@ module XGen
   module Mongo
     module Driver
 
+      # Represents a Mongo database server.
       class Mongo
 
         DEFAULT_PORT = 27017
 
+        # Host default is 'localhost', port default is DEFAULT_PORT.
         def initialize(host='localhost', port=DEFAULT_PORT)
           @host, @port = host, port
         end
 
+        # Return the XGen::Mongo::Driver::DB named +db_name+.
         def db(db_name)
           XGen::Mongo::Driver::DB.new(db_name, @host, @port)
         end
 
+        # Not implemented.
         def clone_database(from)
           raise "not implemented"
         end
 
+        # Not implemented.
         def copy_database(from_host, from_db, to_db)
           raise "not implemented"
         end
diff --git a/lib/mongo/objectid.rb b/lib/mongo/objectid.rb
index b7678dc..0b30115 100644
--- a/lib/mongo/objectid.rb
+++ b/lib/mongo/objectid.rb
@@ -1,3 +1,4 @@
+# ---
 # Copyright (C) 2008 10gen Inc.
 #
 # This program is free software: you can redistribute it and/or modify it
@@ -11,6 +12,7 @@
 #
 # You should have received a copy of the GNU Affero General Public License
 # along with this program. If not, see <http://www.gnu.org/licenses/>.
+# +++
 
 require 'mutex_m'
 require 'mongo/util/byte_buffer'
@@ -19,7 +21,12 @@ module XGen
   module Mongo
     module Driver
 
-      # Implementation of the Babble OID.
+      # Implementation of the Babble OID. Object ids are not required by
+      # Mongo, but they make certain operations more efficient.
+      #
+      # The driver does not automatically assign ids to records that are
+      # inserted. (An upcoming feature will allow you to give an id "factory"
+      # to a database and/or a collection.)
       # 
       #   12 bytes
       #   ---
@@ -65,6 +72,7 @@ module XGen
           @data.collect { |b| '%02x' % b }.join
         end
 
+        # (Would normally be private, but isn't so we can test it.)
         def generate_id(t=nil)
           t ||= Time.new.to_i
           buf = ByteBuffer.new
@@ -80,6 +88,7 @@ module XGen
           buf.to_a.dup
         end
 
+        # (Would normally be private, but isn't so we can test it.)
         def index_for_time(t)
           LOCK.mu_synchronize {
             if t != @@index_time
diff --git a/lib/mongo/query.rb b/lib/mongo/query.rb
index e95ab23..5309c00 100644
--- a/lib/mongo/query.rb
+++ b/lib/mongo/query.rb
@@ -1,3 +1,4 @@
+# ---
 # Copyright (C) 2008 10gen Inc.
 #
 # This program is free software: you can redistribute it and/or modify it
@@ -11,6 +12,7 @@
 #
 # You should have received a copy of the GNU Affero General Public License
 # along with this program. If not, see <http://www.gnu.org/licenses/>.
+# +++
 
 require 'socket'
 require 'mongo/collection'
@@ -20,28 +22,52 @@ module XGen
   module Mongo
     module Driver
 
+      # A query against a collection. A query's selector is a hash. See the
+      # Mongo documentation for query details.
       class Query
 
         attr_accessor :number_to_skip, :number_to_return, :order_by
         attr_reader :selector, :fields # writers defined below
 
+        # sel :: A hash describing the query. See the Mongo docs for details.
+        #
+        # return_fields :: If not +nil+, an array of field names. Only those
+        #                  fields will be returned. (Called :fields in calls
+        #                  to Collection#find.)
+        #
+        # number_to_skip :: Number of records to skip before returning
+        #                   records. (Called :offset in calls to
+        #                   Collection#find.)
+        #
+        # number_to_return :: Max number of records to return. (Called :limit
+        #                     in calls to Collection#find.)
+        #
+        # order_by :: If not +nil+, specifies record return order. Either hash
+        #             of field names as keys and 1/-1 as values; 1 ==
+        #             ascending, -1 == descending, or array of field names
+        #             (all assumed to be sorted in ascending order). (Called
+        #             :sort in calls to Collection#find.)
         def initialize(sel={}, return_fields=nil, number_to_skip=0, number_to_return=0, order_by=nil)
           @number_to_skip, @number_to_return, @order_by = number_to_skip, number_to_return, order_by
           self.selector = sel
           self.fields = return_fields
         end
 
+        # Set query selector hash. If sel is a string, it will be used as a
+        # $where clause. (See Mongo docs for details.)
         def selector=(sel)
           @selector = case sel
                       when nil
                         {}
                       when String
-                        {"$where" => "function() { return #{sel}; }"}
+                        {"$where" => sel}
                       when Hash
                         sel
                       end
         end
 
+        # Set fields to return. If +val+ is +nil+ or empty, all fields will be
+        # returned.
         def fields=(val)
           @fields = val
           @fields = nil if @fields && @fields.empty?
diff --git a/lib/mongo/util/bson.rb b/lib/mongo/util/bson.rb
index 6632d01..87dff7d 100644
--- a/lib/mongo/util/bson.rb
+++ b/lib/mongo/util/bson.rb
@@ -1,9 +1,24 @@
+# ---
+# Copyright (C) 2008 10gen Inc.
+#
+# This program is free software: you can redistribute it and/or modify it
+# under the terms of the GNU Affero General Public License, version 3, as
+# published by the Free Software Foundation.
+#
+# This program is distributed in the hope that it will be useful, but WITHOUT
+# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+# FITNESS FOR A PARTICULAR PURPOSE. See the GNU Affero General Public License
+# for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with this program. If not, see <http://www.gnu.org/licenses/>.
+# +++
+
 require 'mongo/util/byte_buffer'
 require 'mongo/util/ordered_hash'
 require 'mongo/objectid'
 
-# See http://github.com/10gen/mongo/tree/master/db/jsobj.h
-
+# A BSON seralizer/deserializer.
 class BSON
 
   MINKEY = -1
diff --git a/lib/mongo/util/byte_buffer.rb b/lib/mongo/util/byte_buffer.rb
index dcede06..675f8ba 100644
--- a/lib/mongo/util/byte_buffer.rb
+++ b/lib/mongo/util/byte_buffer.rb
@@ -1,3 +1,20 @@
+# ---
+# Copyright (C) 2008 10gen Inc.
+#
+# This program is free software: you can redistribute it and/or modify it
+# under the terms of the GNU Affero General Public License, version 3, as
+# published by the Free Software Foundation.
+#
+# This program is distributed in the hope that it will be useful, but WITHOUT
+# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+# FITNESS FOR A PARTICULAR PURPOSE. See the GNU Affero General Public License
+# for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with this program. If not, see <http://www.gnu.org/licenses/>.
+# +++
+
+# A byte buffer.
 class ByteBuffer
 
   attr_reader :order
diff --git a/lib/mongo/util/ordered_hash.rb b/lib/mongo/util/ordered_hash.rb
index 343a223..af402ce 100644
--- a/lib/mongo/util/ordered_hash.rb
+++ b/lib/mongo/util/ordered_hash.rb
@@ -1,3 +1,20 @@
+# ---
+# Copyright (C) 2008 10gen Inc.
+#
+# This program is free software: you can redistribute it and/or modify it
+# under the terms of the GNU Affero General Public License, version 3, as
+# published by the Free Software Foundation.
+#
+# This program is distributed in the hope that it will be useful, but WITHOUT
+# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+# FITNESS FOR A PARTICULAR PURPOSE. See the GNU Affero General Public License
+# for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with this program. If not, see <http://www.gnu.org/licenses/>.
+# +++
+
+# A hash in which the order of keys are preserved.
 class OrderedHash < Hash
 
   attr_accessor :ordered_keys