* spiders don't have to work on specific domains;
* explain what to use Downloader middleware for
and what to use Spider middleware for;
* Engine no longer locates spiders based on domains;
* "Spider middleware output direction" step was missing.
See also: GH-1569.
See http://www.sphinx-doc.org/en/stable/changes.html#release-1-4-released-mar-28-2016
sphinx_rtd_theme has become optional, needs to be added to reqs
https://github.com/sphinx-doc/sphinx/pull/2320 changes node entries tuples
to 5 values instead of 4
`sh` syntax highlighting added very locally in selectors.rst
because of this warning/error with Sphinx 1.4:
```
Warning, treated as error:
/home/paul/src/scrapy/docs/topics/selectors.rst:743:
WARNING: Could not lex literal_block as "python". Highlighting skipped.
```
* update the scrapy.org example to deal with the new layout.
* replaced slashdot.org by reddit.com, because it seems that slashdot is blocking requests.
* `REDIRECT_MAX_METAREFRESH_DELAY` has been deprecated and was
renamed to `METAREFRESH_MAXDELAY`.
* Merge duplicate documents about `METAREFRESH_MAXDELAY` appeared both
in the settings page and the downloader-middlewares page.
>>> response.xpath('//div/[id="not-exists"]/text()').extract_first() is None
Traceback (most recent call last):
File "<console>", line 1, in <module>
File "/home/vagrant/.virtualenvs/scrapy/lib/python2.7/site-packages/scrapy/http/response/text.py", line 109, in xpath
return self.selector.xpath(query)
File "/home/vagrant/.virtualenvs/scrapy/lib/python2.7/site-packages/scrapy/selector/unified.py", line 100, in xpath
raise ValueError(msg if six.PY3 else msg.encode("unicode_escape"))
ValueError: Invalid XPath: //div/[id="not-exists"]/text()
I've made a few small corrections, some spelling changes and typo fixes.
I've tried to respect regional spelling differences and avoided proposing hyphenating compound words.
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