AS guide: documents Hash#to_xml

1 files changed, 45 insertions, 1 deletions

diff --git a/railties/guides/source/active_support_overview.textile b/railties/guides/source/active_support_overview.textile
index be787b6af2..a4866f18be 100644
--- a/railties/guides/source/active_support_overview.textile
+++ b/railties/guides/source/active_support_overview.textile
@@ -1064,7 +1064,51 @@ NOTE: Observe in the previous example that consecutive separators result in empt
 
 h3. Extensions to +Hash+
 
-...
+h4. Conversions
+
+h5. +to_xml+
+
+The method +to_xml+ returns a string containing an XML representation of its receiver:
+
+<ruby>
+{"foo" => 1, "bar" => 2}.to_xml
+# =>
+# <?xml version="1.0" encoding="UTF-8"?>
+# <hash>
+#   <foo type="integer">1</foo>
+#   <bar type="integer">2</bar>
+# </hash>
+</ruby>
+
+To do so, the method loops over the pairs and builds nodes that depend on the _values_. Given a pair +key+, +value+:
+
+* If +value+ is a hash there's a recursive call with +key+ as <tt>:root</tt>.
+
+* If +value+ is an array there's a recursive call with +key+ as <tt>:root</tt>, and +key+ singularized as <tt>:children</tt>.
+
+* If +value+ is a callable object it must expect one or two arguments. Depending on the arity, the callable is invoked with the +options+ hash as first argument with +key+ as <tt>:root</tt>, and +key+ singularized as second argument. Its return value becomes a new node.
+
+* If +value+ responds to +to_xml+ the method is invoked with +key+ as <tt>:root</tt>.
+
+* Otherwise, a node with +key+ as tag is created with a string representation of +value+ as text node. If +value+ is +nil+ an attribute "nil" set to "true" is added. Unless the option <tt>:skip_types</tt> exists and is true, an attribute "type" is added as well according to the following mapping:
+<ruby>
+XML_TYPE_NAMES = {
+  "Symbol"     => "symbol",
+  "Fixnum"     => "integer",
+  "Bignum"     => "integer",
+  "BigDecimal" => "decimal",
+  "Float"      => "float",
+  "TrueClass"  => "boolean",
+  "FalseClass" => "boolean",
+  "Date"       => "date",
+  "DateTime"   => "datetime",
+  "Time"       => "datetime"
+}
+</ruby>
+
+By default the root node is "hash", but that's configurable via the <tt>:root</tt> option.
+
+The default XML builder is a fresh instance of <tt>Builder::XmlMarkup</tt>. You can configure your own builder with the <tt>:builder</tt> option. The method also accepts options like <tt>:dasherize</tt> and friends, they are forwarded to the builder.
 
 h3. Extensions to +Range+