Support for the XPath "<" operator.

lib/oga/xpath/evaluator.rb

@@ -754,6 +754,22 @@ module Oga
         return !on_eq(ast_node, context)
       end
 
+      ##
+      # Processes the `<` operator.
+      #
+      # This operator converts the left and right expression to a number and
+      # returns `true` if the first number is lower than the second number.
+      #
+      # @param [Oga::XML::Node] ast_node
+      # @param [Oga::XML::NodeSet] context
+      # @return [TrueClass|FalseClass]
+      #
+      def on_lt(ast_node, context)
+        left, right = *ast_node
+
+        return on_call_number(context, left) < on_call_number(context, right)
+      end
+
       ##
       # Delegates function calls to specific handlers.
       #

spec/oga/xpath/evaluator/operators/lt_spec.rb

@@ -0,0 +1,42 @@
+require 'spec_helper'
+
+describe Oga::XPath::Evaluator do
+  context 'lower-than operator' do
+    before do
+      @document  = parse('<root><a>10</a><b>20</b></root>')
+      @evaluator = described_class.new(@document)
+    end
+
+    example 'return true if a number is lower than another number' do
+      @evaluator.evaluate('10 < 20').should == true
+    end
+
+    example 'return false if a number is not lower than another number' do
+      @evaluator.evaluate('20 < 10').should == false
+    end
+
+    example 'return true if a number is lower than a string' do
+      @evaluator.evaluate('10 < "20"').should == true
+    end
+
+    example 'return true if a string is lower than a number' do
+      @evaluator.evaluate('"10" < 20').should == true
+    end
+
+    example 'return true if a string is lower than another string' do
+      @evaluator.evaluate('"10" < "20"').should == true
+    end
+
+    example 'return true if a number is lower than a node set' do
+      @evaluator.evaluate('10 < root/b').should == true
+    end
+
+    example 'return true if a string is lower than a node set' do
+      @evaluator.evaluate('"10" < root/b').should == true
+    end
+
+    example 'return true if a node set is lower than another node set' do
+      @evaluator.evaluate('root/a < root/b').should == true
+    end
+  end
+end