docs: adds another spider example that yields multiples requests/items from a single callback

docs/topics/spiders.rst

@@ -169,6 +169,31 @@ Let's see an example::
 
     SPIDER = MySpider()
 
+Another example returning multiples Requests and Items from a single callback::
+
+    from scrapy.selector import HtmlXPathSelector
+    from scrapy.spider import BaseSpider
+    from scrapy.http import Request
+    from myproject.items import MyItem
+
+    class MySpider(BaseSpider):
+        domain_name = 'http://www.example.com'
+        start_urls = [
+            'http://www.example.com/1.html',
+            'http://www.example.com/2.html',
+            'http://www.example.com/3.html',
+        ]
+
+        def parse(self, response):
+            hxs = HtmlXPathSelector(response)
+            for h3 in hxs.select('//h3').extract():
+                yield MyItem(title=h3)
+
+            for url in hxs.select('//a/@href').extract():
+                yield Request(url, callback=self.parse)
+
+    SPIDER = MySpider()
+
 .. module:: scrapy.contrib.spiders
    :synopsis: Collection of generic spiders