diff --git a/lib/oga/xpath/evaluator.rb b/lib/oga/xpath/evaluator.rb
index 9d4df4b..058c797 100644
--- a/lib/oga/xpath/evaluator.rb
+++ b/lib/oga/xpath/evaluator.rb
@@ -354,6 +354,33 @@ module Oga
return nodes
end
+ ##
+ # Evaluates the `preceding-sibling` axis.
+ #
+ # @param [Oga::XPath::Node] ast_node
+ # @param [Oga::XML::NodeSet] context
+ # @return [Oga::XML::NodeSet]
+ #
+ def on_axis_preceding_sibling(ast_node, context)
+ nodes = XML::NodeSet.new
+
+ context.each do |context_node|
+ check = true
+ parent = has_parent?(context_node) ? context_node.parent : nil
+
+ @document.each_node do |doc_node|
+ # Test everything *until* we hit the current context node.
+ if doc_node == context_node
+ break
+ elsif doc_node.parent == parent and node_matches?(doc_node, ast_node)
+ nodes << doc_node
+ end
+ end
+ end
+
+ return nodes
+ end
+
##
# Returns a node set containing all the child nodes of the given set of
# nodes.
diff --git a/spec/oga/xpath/evaluator/axes/preceding_sibling_spec.rb b/spec/oga/xpath/evaluator/axes/preceding_sibling_spec.rb
new file mode 100644
index 0000000..27b015e
--- /dev/null
+++ b/spec/oga/xpath/evaluator/axes/preceding_sibling_spec.rb
@@ -0,0 +1,33 @@
+require 'spec_helper'
+
+describe Oga::XPath::Evaluator do
+ context 'preceding-sibling axis' do
+ before do
+ @document = parse(<<-EOF.strip.gsub(/\s+/m, ''))
+
+
+
+
+
+
+
+
+ EOF
+
+ @second_foo = @document.children[0].children[1].children[0]
+ @evaluator = described_class.new(@document)
+ end
+
+ context 'matching nodes in the current context' do
+ before do
+ @set = @evaluator.evaluate('root/bar/baz/preceding-sibling::foo')
+ end
+
+ it_behaves_like :node_set, :length => 1
+
+ example 'return the second node' do
+ @set[0].should == @second_foo
+ end
+ end
+ end
+end