ambiguous_steps.rb

Then /^I should see ([^"]+)$/ do |thing|
  page.should have_css(selector_for(thing))
end

When /^(.*) within ([^:"]+)$/ do |step, parent|
  with_scope(parent) { When step }
end

area_selector.rb

when 'the cart summary'
  '#cart_summary'

error.txt

      Ambiguous match of "I should see the 1st design within the cart summary":
      
      features/step_definitions/navigation_steps.rb:69:in `/^I should see ([^"]+)$/'
      features/step_definitions/web_steps.rb:21:in `/^(.*) within ([^:"]+)$/'
      
      You can run again with --guess to make Cucumber be more smart about it
       (Cucumber::Ambiguous)

unambiguous_step.rb

Then /^I should see ((?:(?!within|").)+)$/ do |thing|
  page.should have_css(selector_for(thing))
end