Allow querying of nodes using CSS.

lib/oga/xml/querying.rb

@@ -27,6 +27,30 @@ module Oga
 
         return result.is_a?(XML::NodeSet) ? result.first : result
       end
+
+      ##
+      # Evaluates the given CSS expression.
+      #
+      # @param [String] expression The CSS expression to run.
+      # @see [Oga::XPath::Evaluator#initialize]
+      #
+      def css(expression)
+        ast = CSS::Parser.new(expression).parse
+
+        return XPath::Evaluator.new(self).evaluate_ast(ast)
+      end
+
+      ##
+      # Evaluates the given CSS expression and returns the first node in the
+      # set.
+      #
+      # @see [#css]
+      #
+      def at_css(*args)
+        result = css(*args)
+
+        return result.is_a?(XML::NodeSet) ? result.first : result
+      end
     end # Querying
   end # XML
 end # Oga

spec/oga/xml/querying_spec.rb

@@ -32,4 +32,16 @@ describe Oga::XML::Querying do
       @document.at_xpath('$number', 'number' => 10).should == 10
     end
   end
+
+  context '#css' do
+    example 'query a document' do
+      @document.css('a').should == @document.children
+    end
+  end
+
+  context '#at_css' do
+    example 'query a document' do
+      @document.at_css('a').should == @document.children[0]
+    end
+  end
 end