Parsing support for the :only-of-type pseudo.

lib/oga/css/parser.y

@@ -541,6 +541,15 @@ end
     return s(:and, on_pseudo_class_first_child, on_pseudo_class_last_child)
   end
 
+  ##
+  # Generates the AST for the `:only-of-type` selector.
+  #
+  # @return [AST::Node]
+  #
+  def on_pseudo_class_only_of_type
+    return s(:eq, s(:call, 'last'), s(:int, 1))
+  end
+
   private
 
   ##

spec/oga/css/parser/pseudo_classes/only_of_type_spec.rb

@@ -0,0 +1,11 @@
+require 'spec_helper'
+
+describe Oga::CSS::Parser do
+  context ':only-of-type pseudo class' do
+    example 'parse the :only-of-type pseudo class' do
+      parse_css(':only-of-type').should == parse_xpath(
+        'descendant-or-self::*[last() = 1]'
+      )
+    end
+  end
+end