title: Scrapy response.xpath not returning anything for a query
body: <p>I am using the scrapy shell to extract some text data. Here are the commands i gave in the scrapy shell:</p>
  
  <pre><code>&gt;&gt;&gt; scrapy shell "http://jobs.parklandcareers.com/dallas/nursing/jobid6541851-nurse-resident-cardiopulmonary-icu-feb2015-nurse-residency-requires-contract-jobs"
  
  &gt;&gt;&gt; response.xpath('//*[@id="jobDesc"]/span[1]/text()')
  [&lt;Selector xpath='//*[@id="jobDesc"]/span[1]/text()' data=u'Dallas, TX'&gt;]
  &gt;&gt;&gt; response.xpath('//*[@id="jobDesc"]/span[2]/p/text()[2]')
  [&lt;Selector xpath='//*[@id="jobDesc"]/span[2]/p/text()[2]' data=u'Responsible for attending assigned nursi'&gt;]
  &gt;&gt;&gt; response.xpath('//*[@id="jobDesc"]/span[2]/p/text()[preceding-sibling::*="Education"][following-sibling::*="Certification"]')
  []
  </code></pre>
  
  <p>The third command is not returning any data. I was trying to extract data between 2 keywords in the command. Where am i wrong?</p>