diff --git a/beetsplug/zero.py b/beetsplug/zero.py
index b97c37bcd..561430ddc 100644
--- a/beetsplug/zero.py
+++ b/beetsplug/zero.py
@@ -42,7 +42,7 @@ class ZeroPlugin(BeetsPlugin):
         self.config.add({
             'fields': [],
             'keep_fields': [],
-            'update_database': False
+            'update_database': False,
         })
 
         self.patterns = {}
@@ -51,7 +51,7 @@ class ZeroPlugin(BeetsPlugin):
         if self.config['fields']:
             self.validate_config('fields')
             for field in self.config['fields'].as_str_seq():
-                self.write_patterns(field)
+                self.set_pattern(field)
 
         elif self.config['keep_fields']:
             self.validate_config('keep_fields')
@@ -59,7 +59,7 @@ class ZeroPlugin(BeetsPlugin):
             for field in MediaFile.fields():
                 if field in self.config['keep_fields'].as_str_seq():
                     continue
-                self.write_patterns(field)
+                self.set_pattern(field)
 
             # These fields should be preserved
             for key in ('id', 'path', 'album_id'):
@@ -79,7 +79,10 @@ class ZeroPlugin(BeetsPlugin):
                                u'it would be dangerous', field)
                 continue
 
-    def write_patterns(self, field):
+    def set_pattern(self, field):
+        """Set a field in `self.patterns` to a string list corresponding to
+        the configuration, or `True` if the field has no specific configuration.
+        """
         try:
             self.patterns[field] = self.config[field].as_str_seq()
         except confit.NotFoundError:
diff --git a/docs/plugins/zero.rst b/docs/plugins/zero.rst
index 360c737a5..cc70e6675 100644
--- a/docs/plugins/zero.rst
+++ b/docs/plugins/zero.rst
@@ -2,10 +2,8 @@ Zero Plugin
 ===========
 
 The ``zero`` plugin allows you to null fields in files' metadata tags. Fields
-can be nulled unconditionally or conditioned on a pattern match. It works in
-two independent modes - blacklist and whitelist. You can only choose one option,
-however blacklist is the default. For example, the plugin can strip useless
-comments like "ripped by MyGreatRipper."
+can be nulled unconditionally or conditioned on a pattern match. For example,
+the plugin can strip useless comments like "ripped by MyGreatRipper."
 
 To use the ``zero`` plugin, enable the plugin in your configuration
 (see :ref:`using-plugins`).
@@ -20,9 +18,9 @@ fields to nullify and the conditions for nullifying them:
   get the list of all available fields by running ``beet fields``. In
   addition, the ``images`` field allows you to remove any images
   embedded in the media file.
-* Set ``keep_fields`` respectively to list of fields that plugin should
-  preserve. That way ``zero`` cleans anything other than fields written in this
-  option.
+* Set ``keep_fields`` to *invert* the logic of the plugin. Only these fields
+  will be kept; other fields will be removed. Remember to set only
+  ``fields`` or ``keep_fields``, not both!
 * To conditionally filter a field, use ``field: [regexp, regexp]`` to specify
   regular expressions.
 * By default this plugin only affects files' tags ; the beets database is left
@@ -36,6 +34,10 @@ For example::
         genre: [rnb, 'power metal']
         update_database: true
 
+The plugin can work in one of two modes. The first mode, the default,
+is a blacklist, where you choose the tags you want to remove. The second mode
+is a whitelist where you instead specify the tags you want to keep.
+
 If a custom pattern is not defined for a given field, the field will be nulled
 unconditionally.