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structure of an atom feed in xml chapter
This commit is contained in:
Mark Pilgrim
+9
-10
@@ -1,17 +1,16 @@
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<?xml version="1.0" encoding="utf-8"?>
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<feed xmlns="http://www.w3.org/2005/Atom" xml:lang="en">
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<title type="text">dive into mark</title>
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<subtitle type="text">currently between addictions</subtitle>
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<title>dive into mark</title>
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<subtitle>currently between addictions</subtitle>
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<id>tag:diveintomark.org,2001-07-29:/</id>
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<updated>2009-03-27T21:56:07Z</updated>
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<link rel="alternate" type="text/html" href="http://diveintomark.org/"/>
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<link rel="self" href="http://diveintomark.org/feed/" type="application/atom+xml"/>
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<entry>
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<author>
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<name>Mark</name>
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<uri>http://diveintomark.org/</uri>
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</author>
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<title type="html"><![CDATA[Dive into history, 2009 edition]]></title>
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<title>Dive into history, 2009 edition</title>
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<link rel="alternate" type="text/html"
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href="http://diveintomark.org/archives/2009/03/27/dive-into-history-2009-edition"/>
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<id>tag:diveintomark.org,2009-03-27:/archives/20090327172042</id>
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@@ -20,16 +19,17 @@
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<category scheme="http://diveintomark.org" term="diveintopython"/>
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<category scheme="http://diveintomark.org" term="docbook"/>
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<category scheme="http://diveintomark.org" term="html"/>
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<summary type="html">Putting an entire chapter on one page sounds bloated, but
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consider this: my longest chapter so far would be 75 printed pages, and it
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loads in under 5 seconds. On dialup.</summary>
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<summary type="html">Putting an entire chapter on one page sounds
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bloated, but consider this &mdash; my longest chapter so far
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would be 75 printed pages, and it loads in under 5 seconds&hellip;
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On dialup.</summary>
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</entry>
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<entry>
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<author>
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<name>Mark</name>
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<uri>http://diveintomark.org/</uri>
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</author>
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<title type="html"><![CDATA[Accessibility is a harsh mistress]]></title>
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<title>Accessibility is a harsh mistress</title>
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<link rel="alternate" type="text/html"
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href="http://diveintomark.org/archives/2009/03/21/accessibility-is-a-harsh-mistress"/>
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<id>tag:diveintomark.org,2009-03-21:/archives/20090321200928</id>
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@@ -44,8 +44,7 @@
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<name>Mark</name>
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<uri>http://diveintomark.org/</uri>
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</author>
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<title type="html"><![CDATA[A gentle introduction to video encoding,
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part 1: container formats]]></title>
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<title>A gentle introduction to video encoding, part 1: container formats</title>
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<link rel="alternate" type="text/html"
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href="http://diveintomark.org/archives/2008/12/18/give-part-1-container-formats"/>
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<id>tag:diveintomark.org,2008-12-18:/archives/20081218155422</id>
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@@ -25,18 +25,18 @@ mark{display:inline}
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<p class=d>[<a href=examples/feed.xml>download <code>feed.xml</code></a>]
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<pre><code><?xml version="1.0" encoding="utf-8"?>
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<feed xmlns="http://www.w3.org/2005/Atom" xml:lang="en">
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<title type="text">dive into mark</title>
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<subtitle type="text">currently between addictions</subtitle>
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<title>dive into mark</title>
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<subtitle>currently between addictions</subtitle>
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<id>tag:diveintomark.org,2001-07-29:/</id>
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<updated>2009-03-27T21:56:07Z</updated>
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<link rel="alternate" type="text/html" href="http://diveintomark.org/"/>
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<link rel="self" href="http://diveintomark.org/feed/" type="application/atom+xml"/>
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<link rel="self" type="application/atom+xml" href="http://diveintomark.org/feed/"/>
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<entry>
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<author>
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<name>Mark</name>
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<uri>http://diveintomark.org/</uri>
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</author>
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<title type="html"><![CDATA[Dive into history, 2009 edition]]></title>
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<title>Dive into history, 2009 edition</title>
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<link rel="alternate" type="text/html"
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href="http://diveintomark.org/archives/2009/03/27/dive-into-history-2009-edition"/>
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<id>tag:diveintomark.org,2009-03-27:/archives/20090327172042</id>
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@@ -45,16 +45,17 @@ mark{display:inline}
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<category scheme="http://diveintomark.org" term="diveintopython"/>
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<category scheme="http://diveintomark.org" term="docbook"/>
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<category scheme="http://diveintomark.org" term="html"/>
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<summary type="html">Putting an entire chapter on one page sounds bloated, but
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consider this: my longest chapter so far would be 75 printed pages, and it
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loads in under 5 seconds. On dialup.</summary>
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<summary type="html">Putting an entire chapter on one page sounds
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bloated, but consider this &amp;mdash; my longest chapter so far
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would be 75 printed pages, and it loads in under 5 seconds&amp;hellip;
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On dialup.</summary>
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</entry>
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<entry>
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<author>
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<name>Mark</name>
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<uri>http://diveintomark.org/</uri>
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</author>
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<title type="html"><![CDATA[Accessibility is a harsh mistress]]></title>
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<title>Accessibility is a harsh mistress</title>
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<link rel="alternate" type="text/html"
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href="http://diveintomark.org/archives/2009/03/21/accessibility-is-a-harsh-mistress"/>
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<id>tag:diveintomark.org,2009-03-21:/archives/20090321200928</id>
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@@ -69,8 +70,7 @@ mark{display:inline}
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<name>Mark</name>
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<uri>http://diveintomark.org/</uri>
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</author>
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<title type="html"><![CDATA[A gentle introduction to video encoding,
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part 1: container formats]]></title>
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<title>A gentle introduction to video encoding, part 1: container formats</title>
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<link rel="alternate" type="text/html"
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href="http://diveintomark.org/archives/2008/12/18/give-part-1-container-formats"/>
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<id>tag:diveintomark.org,2008-12-18:/archives/20081218155422</id>
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@@ -102,14 +102,19 @@ mark{display:inline}
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<li>This is the matching <i>end tag</i> of the <code>foo</code> element. Like balancing parentheses in writing or mathematics or code, every start tag much be <i>closed</i> (matched) by a corresponding end tag.
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</ol>
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<p>Elements can be <i>nested</i>. An element <code>bar</code> inside an element <code>foo</code> is said to be a <i>subelement</i> or <i>child</i> of <code>foo</code>.
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<p>Elements can be <i>nested</i> to any depth. An element <code>bar</code> inside an element <code>foo</code> is said to be a <i>subelement</i> or <i>child</i> of <code>foo</code>.
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<pre class=nd><code><foo>
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<mark><bar></bar></mark>
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</foo>
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</code></pre>
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<p>Elements can have <i>attributes</i>, which are name-value pairs. Attributes are listed within the start tag of an element. <i>Attribute names</i> can not be repeated within an element. <i>Attribute values</i> must be quoted.
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<p>The first element in every XML document is called the <i>root element</i>. An XML document can only have one root element. The following is <strong>not an XML document</strong>, because it has two root elements:
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<pre class=nd><code><foo></foo>
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<bar></bar></code></pre>
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<p>Elements can have <i>attributes</i>, which are name-value pairs. Attributes are listed within the start tag of an element and separated by whitespace. <i>Attribute names</i> can not be repeated within an element. <i>Attribute values</i> must be quoted.
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<pre class=nd><code><a><foo <mark>lang="en"</mark>> <span>①</span></a>
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<a> <bar <mark>lang="fr"</mark>></bar> <span>②</span></a>
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@@ -161,13 +166,83 @@ mark{display:inline}
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<p>As far as an XML parser is concerned, the previous two XML documents are <em>identical</em>. Namespace + element name = XML identity. Prefixes only exist to refer to namespaces, so the actual prefix name (<code>atom:</code>) is irrelevant. The namespaces match, the element names match, the attributes (or lack of attributes) match, and each element’s text content matches, therefore the XML documents are the same.
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<p>Finally, XML documents can contain <a href=strings.html#one-ring-to-rule-them-all>character encoding information</a> on the first line, before the root element. (If you’re curious how a document can contain information which needs to be known before the document can be parsed, <a href=http://www.w3.org/TR/REC-xml/#sec-guessing-no-ext-info>Section F of the XML specification</a> details how to resolve this Catch-22.)
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<pre class=nd><code><?xml version="1.0" <mark>encoding="utf-8"</mark>?></code></pre>
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<p>And now you know just enough XML to be dangerous!
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<h2 id=xml-structure>The Structure Of An Atom Feed</h2>
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<p>Think of a weblog, or in fact any website with frequently updated content, like <a href=http://www.cnn.com/>CNN.com</a>. The site itself has a title (“CNN.com”), a subtitle (“Breaking News, U.S., World, Weather, Entertainment <i class=baa>&</i> Video News”), a last-updated date (“updated 12:43 p.m. EDT, Sat May 16, 2009”), and a list of articles posted at different times. Each article also has a title, a first-published date (and maybe also a last-updated date, if they published a correction or fixed a typo), and a unique URL.
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<p>The Atom syndication format is designed to capture all of this information in a standard format. My weblog and CNN.com are wildly different in design, scope, and audience, but they both have the same basic structure. CNN.com has a title; my blog has a title. CNN.com publishes articles; I publish articles.
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<p>At the top level is the “root” element, which every Atom feed shares: the <code><feed></code> element in the Atom namespace (<code>http://www.w3.org/2005/Atom</code>). ... FIXME
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<p>At the top level is the <i>root element</i>, which every Atom feed shares: the <code>feed</code> element in the <code>http://www.w3.org/2005/Atom</code> namespace.
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<pre class=nd><code>
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<a><feed xmlns="http://www.w3.org/2005/Atom" <span>①</span></a>
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<a> xml:lang="en"> <span>②</span></a></code></pre>
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<ol>
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<li><code>http://www.w3.org/2005/Atom</code> is the Atom namespace.
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<li>Any element can contain an <code>xml:lang</code> attribute, which declares the language of the element and its children. In this case, the <code>xml:lang</code> attribute is declared once on the root element, which means the entire feed is in English.
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</ol>
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<p>An Atom feed contains several pieces of information about the feed itself. These are declared as children of the root-level <code>feed</code> element.
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<pre class=nd><code><feed xmlns="http://www.w3.org/2005/Atom" xml:lang="en">
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<a> <title>dive into mark</title> <span>①</span></a>
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<a> <subtitle>currently between addictions</subtitle> <span>②</span></a>
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<a> <id>tag:diveintomark.org,2001-07-29:/</id> <span>③</span></a>
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<a> <updated>2009-03-27T21:56:07Z</updated> <span>④</span></a>
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<a> <link rel="alternate" type="text/html" href="http://diveintomark.org/"/> <span>⑤</span></a></code></pre>
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<ol>
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<li>The title of this feed is <code>dive into mark</code>.
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<li>The subtitle of this feed is <code>currently between addictions</code>.
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<li>Every feed needs a globally unique identifier. See <a href=http://www.ietf.org/rfc/rfc4151.txt>RFC 4151</a> for how to create one.
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<li>This feed was last updated on March 27, 2009, at 21:56 GMT. This is usually equivalent to the last-modified date of the most recent article.
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<li>Now things start to get interesting. This <code>link</code> element has no text content, but it has three attributes: <code>rel</code>, <code>type</code>, and <code>href</code>. The <code>rel</code> value tells you what kind of link this is; <code>rel="alternate"</code> means that this is a link to an alternate representation of this feed. The <code>type="text/html"</code> attribute means that this is a link to an HTML page. And the link target is given in the <code>href</code> attribute.
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</ol>
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<p>Now we know that this is a feed for a site named “dive into mark“ which is available at <a href=http://diveintomark.org/><code>http://diveintomark.org/</code></a> and was last updated on March 27, 2009.
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<blockquote class=note>
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<p><span>☞</span>Although the order of elements can be relevant in some XML documents, it is not relevant in an Atom feed.
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</blockquote>
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<p>After the feed-level metadata is the list of the most recent articles. An article looks like this:
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<pre class=nd><code><entry>
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<a> <author> <span>①</span></a>
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<name>Mark</name>
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<uri>http://diveintomark.org/</uri>
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</author>
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<a> <title>Dive into history, 2009 edition</title> <span>②</span></a>
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<a> <link rel="alternate" type="text/html" <span>③</span></a>
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href="http://diveintomark.org/archives/2009/03/27/dive-into-history-2009-edition"/>
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<a> <id>tag:diveintomark.org,2009-03-27:/archives/20090327172042</id> <span>④</span></a>
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<a> <updated>2009-03-27T21:56:07Z</updated> <span>⑤</span></a>
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<published>2009-03-27T17:20:42Z</published>
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<a> <category scheme="http://diveintomark.org" term="diveintopython"/> <span>⑥</span></a>
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<category scheme="http://diveintomark.org" term="docbook"/>
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<category scheme="http://diveintomark.org" term="html"/>
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<a> <summary type="html">Putting an entire chapter on one page sounds <span>⑦</span></a>
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bloated, but consider this &amp;mdash; my longest chapter so far
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would be 75 printed pages, and it loads in under 5 seconds&amp;hellip;
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On dialup.</summary>
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<a></entry> <span>⑧</span></a></code></pre>
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<ol>
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<li>The <code>author</code> element tells who wrote this article: some guy named Mark, whom you can find loafing at <code>http://diveintomark.org/</code>. (This is the same as the alternate link in the feed metadata, but it doesn’t have to be. Many weblogs have multiple authors, each with their own personal website.)
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<li>The <code>title</code> element gives the title of the article, “Dive into history, 2009 edition”.
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<li>As with the feed-level alternate link, this <code>link</code> element gives the address of the HTML version of this article.
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<li>Entries, like feeds, need a unique identifier.
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<li>Entries have two dates: a first-published date (<code>published</code>) and a last-modified date (<code>updated</code>).
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<li>Entries can have an arbitrary number of categories. This article is filed under <code>diveintopython</code>, <code>docbook</code>, and <code>html</code>.
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<li>The <code>summary</code> element gives a brief summary of the article. (There is also a <code>content</code> element, not shown here, if you want to include the complete article text in your feed.) This <code>summary</code> element has the Atom-specific <code>type="html"</code> attribute, which specifies that this summary is a snippet of HTML, not plain text. This is important, since it has HTML-specific entities in it (<code>&mdash;</code> and <code>&hellip;</code>) which should be rendered as “—” and “…” rather than displayed directly.
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<li>Finally, the end tag for the <code>entry</code> element, signaling the end of the metadata for this article.
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</ol>
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<p>
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<h2 id=xml-parse>Parsing XML</h2>
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@@ -322,7 +397,7 @@ from here on out, use lxml.etree explicitly because these functions are specific
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<feed xmlns="http://www.w3.org/2005/Atom" xml:lang="en"><title type="html">dive into mark</title></feed>
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>>> print(lxml.etree.tounicode(new_feed, pretty_print=True))
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<feed xmlns="http://www.w3.org/2005/Atom" xml:lang="en">
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<title type="html">dive into mark</title>
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<title type="html">dive into mark</title>
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</feed>
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</pre>
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