diff --git a/lib/acts_as_span/no_overlap_validator.rb b/lib/acts_as_span/no_overlap_validator.rb
index 5657984..90cf05b 100644
--- a/lib/acts_as_span/no_overlap_validator.rb
+++ b/lib/acts_as_span/no_overlap_validator.rb
@@ -1,51 +1,83 @@
+# frozen_string_literal: true
+
 require 'active_model'
 
 module ActsAsSpan
+  # Validator that checks whether a record is overlapping with others
+  #
+  # Takes options `:instance_scope` (optional) and `:scope` (required):
+  # * `instance_scope` is a proc which, when evaluated by the record, returns
+  #   a boolean value. When false, the validatior will not check for overlap.
+  #   When true, the validator checks normally.
+  # * `scope` is also a proc. This is must return an ActiveRecord Relation that
+  #   determines which records' spans to compare.
+  #
+  # Usage:
+  # Given a record with `siblings` defined, the most basic use case is:
+  # ```
+  # validates_with ActsAsSpan::NoOverlapValidator,
+  #   scope: proc { siblings }
+  # ```
+  # When this record is validated, every record in the ActiveRecord relation
+  #   `record.siblings` is checked for mutual overlap with `record`.
+  #
+  # Use `instance_scope` if there is some condition where a record oughtn't be
+  #   validated for whatever reason:
+  # ```
+  # validates_with ActsAsSpan::NoOverlapValidator,
+  #   scope: proc { siblings }, instance_scope: proc { favorite? }
+  # ```
+  # Now, when this record is validated, if `record.favorite?` is `true`,
+  #   `record` must pass the overlap check with its siblings.
+  #   If `record.favorite?` is `false`, it is under less scrutiny.
+  #
   class NoOverlapValidator < ActiveModel::Validator
     def validate(record)
       overlapping_records = temporally_overlapping_for(record)
       instance_scope = if options[:instance_scope].is_a? Proc
-                         record.instance_eval&options[:instance_scope]
+                         record.instance_eval(&options[:instance_scope])
                        else
                          true
                        end
 
-      if overlapping_records.any? && instance_scope
-
-        record.errors.add(
-          :base,
-          :no_overlap,
-          model_name: record.class.model_name.human,
-          model_name_plural: record.class.model_name.plural.humanize,
-          start_date: record.span.start_date,
-          end_date: record.span.end_date,
-          count: overlapping_records.size,
-          overlapping_records_s: overlapping_records.join(",")
-        )
-      end
+      return unless overlapping_records.any? && instance_scope
+
+      record.errors.add(
+        :base,
+        :no_overlap,
+        model_name: record.class.model_name.human,
+        model_name_plural: record.class.model_name.plural.humanize,
+        start_date: record.span.start_date,
+        end_date: record.span.end_date,
+        count: overlapping_records.size,
+        overlapping_records_s: overlapping_records.join(', ')
+      )
     end
 
-    #TODO add back condition for start_date nil
-    #TODO add support for multiple spans (currently only checks :default)
+    # TODO: add back condition for start_date nil
+    # TODO: add support for multiple spans (currently only checks :default)
     def temporally_overlapping_for(record)
       scope = record.instance_eval(&options[:scope])
 
       start_date = record.span.start_date || Date.current
+
       end_date = record.span.end_date
+      end_field = record.span.end_field
+
       arel_table = record.class.arel_table
 
       if end_date
         scope.where(
           arel_table[record.span.start_field].lteq(end_date)
           .and(
-            arel_table[record.span.end_field].gteq(start_date)
-          .or(arel_table[record.span.end_field].eq(nil))
+            arel_table[end_field].gteq(start_date)
+          .or(arel_table[end_field].eq(nil))
           )
         )
       else
         scope.where(
-          arel_table[record.span.end_field].gteq(start_date)
-          .or(arel_table[record.span.end_field].eq(nil))
+          arel_table[end_field].gteq(start_date)
+          .or(arel_table[end_field].eq(nil))
         )
       end
     end
diff --git a/spec/lib/no_overlap_validator_spec.rb b/spec/lib/no_overlap_validator_spec.rb
index d0eeef1..3efa465 100644
--- a/spec/lib/no_overlap_validator_spec.rb
+++ b/spec/lib/no_overlap_validator_spec.rb
@@ -42,6 +42,29 @@
 
   let(:all_siblings) { [brother, sister, brother_from_another_mother] }
 
+  describe 'instance_scope' do
+    let(:child_class) { OneParentChild }
+
+    let(:new_child_start_date) { Date.current - 2 }
+    let(:new_child_end_date) { Date.current + 3 }
+
+    before { new_child.favorite = favorite }
+
+    context 'when instance_scope evaluates to false' do
+      let(:favorite) { false }
+      it 'skips validation on the record for which instance_scope is false' do
+        expect(new_child).to be_valid
+      end
+    end
+
+    context 'when instance_scope evaluates to true' do
+      let(:favorite) { true }
+      it 'validates normally' do
+        expect(new_child).not_to be_valid
+      end
+    end
+  end
+
   describe 'an object with a single parent' do
     let(:child_class) { OneParentChild }
 
diff --git a/spec/spec_models.rb b/spec/spec_models.rb
index 6b7c4c1..ad56760 100644
--- a/spec/spec_models.rb
+++ b/spec/spec_models.rb
@@ -28,14 +28,22 @@
 
     t.date :start_date
     t.date :end_date
+
+    # every one-parent child is a favorite! ...by default
+    t.boolean :favorite, default: true
   end
 
   acts_as_span
 
+  def favorite?
+    favorite
+  end
+
   belongs_to :mama
   has_siblings through: [:mama]
 
-  validates_with ActsAsSpan::NoOverlapValidator, scope: proc { siblings }
+  validates_with ActsAsSpan::NoOverlapValidator,
+    scope: proc { siblings }, instance_scope: proc { favorite? }
   validates_with ActsAsSpan::WithinParentDateSpanValidator, parents: [:mama]
 end