diff --git a/background_scripts/completion.coffee b/background_scripts/completion.coffee
index 39f8a140b..729e86abf 100644
--- a/background_scripts/completion.coffee
+++ b/background_scripts/completion.coffee
@@ -385,7 +385,7 @@ class SearchEngineCompleter
           # immediately.
           return onComplete []
 
-      SearchEngines.complete searchUrl, queryTerms, (searchSuggestions = []) =>
+      CompletionEngines.complete searchUrl, queryTerms, (searchSuggestions = []) =>
         for suggestion in searchSuggestions
           insertText = if custom then "#{keyword} #{suggestion}" else suggestion
           suggestions.push @mkSuggestion insertText, queryTerms, type, mkUrl(suggestion), suggestion, @computeRelevancy, score
diff --git a/background_scripts/search_engines.coffee b/background_scripts/completion_engines.coffee
similarity index 97%
rename from background_scripts/search_engines.coffee
rename to background_scripts/completion_engines.coffee
index 63c61a474..0177806a1 100644
--- a/background_scripts/search_engines.coffee
+++ b/background_scripts/completion_engines.coffee
@@ -13,8 +13,8 @@
 #   3. "parse" - This takes a successful XMLHttpRequest object (the request has completed successfully), and
 #      returns a list of suggestions (a list of strings).
 #
-# The main completion entry point is SearchEngines.complete().  This implements all lookup and caching
-# logic.  It is possible to add new completion engines without changing the SearchEngines infrastructure
+# The main completion entry point is CompletionEngines.complete().  This implements all lookup and caching
+# logic.  It is possible to add new completion engines without changing the CompletionEngines infrastructure
 # itself.
 
 # A base class for common regexp-based matching engines.
@@ -113,7 +113,7 @@ completionEngines = [
   DummySearchEngine
 ]
 
-SearchEngines =
+CompletionEngines =
   debug: true
 
   get: (searchUrl, url, callback) ->
@@ -216,4 +216,4 @@ SearchEngines =
     @mostRecentHandler = null
 
 root = exports ? window
-root.SearchEngines = SearchEngines
+root.CompletionEngines = CompletionEngines
diff --git a/lib/utils.coffee b/lib/utils.coffee
index 1b2a7a3fa..e97872f0d 100644
--- a/lib/utils.coffee
+++ b/lib/utils.coffee
@@ -207,14 +207,14 @@ globalRoot.extend = (hash1, hash2) ->
     hash1[key] = hash2[key]
   hash1
 
-# A simple cache. Entries used within an expiry period are retained (for one more expiry period), otherwise
-# they are discarded.
+# A simple cache. Entries used within two expiry periods are retained, otherwise they are discarded.
+# At most 2 * @entries entries are retained.
 class SimpleCache
   # expiry: expiry time in milliseconds (default, one hour)
   # entries: maximum number of entries in @cache (there may be this many entries in @previous, too)
   constructor: (@expiry = 60 * 60 * 1000, @entries = 1000) ->
     @cache = {}
-    @rotate() # Force starts the rotation timer.
+    @rotate() # Force start the rotation timer.
 
   rotate: ->
     @previous = @cache
diff --git a/manifest.json b/manifest.json
index d3f6249f3..195d16c88 100644
--- a/manifest.json
+++ b/manifest.json
@@ -14,7 +14,7 @@
       "background_scripts/sync.js",
       "background_scripts/settings.js",
       "background_scripts/exclusions.js",
-      "background_scripts/search_engines.js",
+      "background_scripts/completion_engines.js",
       "background_scripts/completion.js",
       "background_scripts/marks.js",
       "background_scripts/main.js"