From 97e7bb3182f28555d2b5deff01a75d1a87cfd346 Mon Sep 17 00:00:00 2001
From: Stef Busking <stef.busking@gmail.com>
Date: Thu, 13 Jul 2017 16:18:14 +0200
Subject: [PATCH] Only generate an attribute prefix if required

If implemented as specified, the prefix set for an attribute in the DOM
would never be preserved during serialization. This change only
generates the new prefix if the prefix is either missing (which is not
allowed for namespaced attributes), or if it conflicts with another
local namespace definition of the prefix for a different namespace.

Fixes #29
---
 index.html | 18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/index.html b/index.html
index d86da6a..24ae85e 100644
--- a/index.html
+++ b/index.html
@@ -1359,11 +1359,19 @@ <h2>Extensibility</h2>
           "<code>xmlns</code>".
         </ol>
 
-        <li>Otherwise, the <var>attribute namespace</var> in not the <a>XMLNS namespace</a>. Run
-        these steps:
+        <li>Otherwise, the <var>attribute namespace</var> is not the <a>XMLNS namespace</a>. If
+        <var>candidate prefix</var> is null, run these steps:
         <ol>
-          <li>Let <var>candidate prefix</var> be the result of <a>generating a prefix</a> providing
-          <var>map</var>, <var>attribute namespace</var>, and <var>prefix index</var> as input.
+          <li>Let <var>new prefix</var> be <var>attr</var>'s <code><a>prefix</a></code> attribute if it is
+          not <code>null</code> and the <var>local prefixes map</var> does not contain a key matching
+          <var>attr</var>'s <code><a>prefix</a></code>, or the result of <a>generating a prefix</a> providing
+          <var>map</var>, <var>attribute namespace</var>, and <var>prefix index</var> as input otherwise.
+
+          <li><a>Add</a> <var>new prefix</var> to <var>map</var> given namespace <var>attribute namespace</var>.
+
+          <li>Add the value of <var>new prefix</var> as a new key to the <var>local prefixes map</var>, with
+          the <var>attribute namespace</var> as the key's value replacing the value of <code>null</code> with
+          the empty string if applicable.
 
           <li>Append the following to <var>result</var>, in the order listed:
           <ol>
@@ -1371,7 +1379,7 @@ <h2>Extensibility</h2>
 
             <li>The string "<code>xmlns:</code>";
 
-            <li>The value of <var>candidate prefix</var>;
+            <li>The value of <var>new prefix</var>;
 
             <li>"<code>="</code>" (U+003D EQUALS SIGN, U+0022 QUOTATION MARK);