More replaces of references to old sel shortcut

docs/topics/selectors.rst

@@ -141,12 +141,12 @@ method, as follows::
 
 If you want to extract only first matched element, you can call the selector ``.extract_first()``
 
-    >>> sel.xpath('//div[@id="images"]/a/text()').extract_first()
+    >>> response.xpath('//div[@id="images"]/a/text()').extract_first()
     u'Name: My image 1 '
 
 It returns ``None`` if no element was found:
 
-    >>> sel.xpath('//div/[id="not-exists"]/text()').extract_first() is None
+    >>> response.xpath('//div/[id="not-exists"]/text()').extract_first() is None
     True
 
 Notice that CSS selectors can select text or attribute nodes using CSS3
@@ -383,7 +383,7 @@ with groups of itemscopes and corresponding itemprops::
     ...   ...
     ... </div>
     ... """
-    >>>
+    >>> sel = Selector(text=doc, type="html")
     >>> for scope in sel.xpath('//div[@itemscope]'):
     ...     print "current scope:", scope.xpath('@itemtype').extract()
     ...     props = scope.xpath('''