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python-nevow-0.9.32-2mdv2010.0.noarch.rpm

Nevow XML Templates
===================

Stan syntax is cool, but eventually you are going to want to integrate your
Python code with a template designed by an HTML monkey. Nevow accomplishes this
by providing an xmlfile loader which uses the built-in Python SAX libraries to
generate a tree of stan behind the scenes. The general rule is anything that is
possible in stan should be possible in a pure XML template; of course, the XML
syntax is generally going to be much more verbose.

* `loaders.xmlfile`_
* `Nevow's xmlns declaration`_
* `Nevow's Tag Attribute Language`_
* `nevow:render`_
* `Built-in renderers`_
* `nevow:data`_
* `nevow:pattern`_
* `nevow:slot`_
* `nevow:attr`_
* `nevow:invisible`_
* `xmlstr, htmlfile, and htmlstr`_

loaders.xmlfile
---------------

Wherever you have seen a loaders.stan being created in any of the example code,
a loaders.xmlfile can be substituted instead. At the most basic, xmlfile merely
requires the name of an xml template::

  class HelloXML(rend.Page):
      docFactory = loaders.xmlfile('hello.xml')

Placing the following xml in the hello.xml file will cause HelloXML to display a
static page when it is rendered::

  <html>Hello, world!</html>

The following additional keyword arguments may be given to xmlfile to configure
it:

templateDirectory
  The path to the directory which contains the template file. Defaults to ''.

ignoreDocType    
  If True, discard any DOCTYPE declaration when building the DOM from this
  template. When false, preserve the DOCTYPE, causing it to show up in the final
  output. Useful for when you are inserting an XML fragment into a larger page
  and do not wish to generate invalid XML as output. Defaults to False.

ignoreComment
  If True, discard XML comments, causing them to disappear from the output. If
  False, preserve comments and render them in the final output unchanged.
  Defaults to False.

pattern
  If present, the given pattern name will be looked up and used as the root of
  the template. If not present, the entire document will be used as the
  template. Useful for embedding fragments of an XML document in a larger page.
  Defaults to None.

Nevow's xmlns declaration
-------------------------

In order for Nevow to notice and process any XML directives in the template
file, you must declare the Nevow xmlns at the top of your XML document. Nevow's
xmlns is::

  http://nevow.com/ns/nevow/0.1

The syntax for declaring that your xml document uses this namespace is::

  <html xmlns:nevow="http://nevow.com/ns/nevow/0.1"></html>

You may replace the text "nevow" in the above example with any name you choose.
For example, many people use "n" because it is shorter to type. If you do so, be
sure to replace all occurrences of the nevow namespace in the examples with the
namespace name you choose.

Nevow's Tag Attribute Language
------------------------------

The markup you will add to your XHTML file in order to invoke Nevow code
consists mostly of namespaced tag attributes. This approach was influenced
heavily by the Zope Page Templates (ZPT) Tag Attribute Language (TAL). However,
I felt that TAL did not go far enough in removing control flow and branching
possibilities from the XML template. Nevow's main philosophy is that it should
be as easy as possible to move from the XML document into Python code, and that
the Python code should have ultimate control over manipulating the structure of
the XML template.

The key is that it is easy to expose Python methods that you write to your XML
template, and it is easy for the XML templates to mark nodes which it wishes the
Python method to manipulate. In this way, if either the Python implementation
changes or the location or content of the marked nodes change in the XML
template, the other side will be isolated from these changes.

Nevow's XML templating has two attributes which invoke Python code:

* nevow:render -- Invokes a Python method and replaces the template node with the result
* nevow:data -- Invokes a Python method and sets the data special for the node to the result

It has one attribute which marks nodes as manipulatable by Python code:

* nevow:pattern -- Gives a node a name so that Python code may clone and mutate copies of this node

It also has two namespaced tags:

* nevow:slot -- Works in the same way as the slot attribute
* nevow:attr -- Indicates that an attribute of the parent tag should be manipulated by Python code in some way

nevow:render
------------

When the nevow:render attribute is encountered, the xmlfile loader sets the
render special to a directive constructed with the attribute value. When the
template is rendered, this means that the appropriate render_* method will be
looked up on the IRendererFactory (generally the Page instance)::

  <html><div nevow:render="foo" /></html>

With the render_foo method::

  def render_foo(self, ctx, data):
      return "Hello"

Will result in the document::

  <html>Hello</html>

Note that the return value of the render method replaces the template node in
the DOM, so if you want the template node to remain, you should use ctx.tag.

Built-in renderers
------------------

Nevow comes with various built in renderers on the Page class.

data
  Renders the current data as-is inside the current node.

string
  Renders the current data as a string inside the current node.

sequence
  Iterates the current data, copying the "item" pattern for each item. Sets the
  the data special of the new node to the item, and inserts the result in the
  current node. See the nevow.rend.sequence docstring for information about
  other used patterns, including "header", "divider", "footer" and "empty".

mapping
  Calls .items() on the current data, and calls ctx.fillSlots(key, value) for
  every key, value pair in the result. Returns the template tag.

xml
  Inserts the current data into the template after wrapping it in an xml
  instance. Not very useful in practice.

nevow:data
----------

When the nevow:data attribute is encountered, the xmlfile loader sets the data
special of the current node to a directive constructed with the attribute value.
When the template is rendered, this means that the appropriate data_* method
will be looked up on the current IContainer (generally the Page instance). The
data_* method will be called, and the result will be set as the data special of
the current Tag::

  <html><div nevow:data="name" nevow:render="data" /></html>

With the data_name method::

  def data_name(self, ctx, data):
      return "Hello!"

Will result in the document::

  <html><div>Hello!</div></html>

Note that with a data attribute on a node but no renderer, the result of the
data method will be set as the data special for that tag, and child render
methods will be passed this data.

nevow:pattern
-------------

When the nevow:pattern attribute is encountered, the xmlfile loader sets the
pattern special of the current node to the attribute value as a string.
Renderers which are above this node may then make copies of it using the
nevow.inevow.IQ of the current context. With the template::

  <html nevow:render="stuff"><div nevow:pattern="somePattern" nevow:render="data" /></html>

And the renderer::

  def render_stuff(self, ctx, data):
      pat = inevow.IQ(ctx).patternGenerator('somePattern')
      return [pat(data=1), pat(data=2)]

Will result in the document::

  <html><div>1</div><div>2</div></html>

nevow:slot
----------

When the nevow:slot tag is encountered, the xmlfile loader constructs a
nevow.stan.slot instance, passing the name attribute value as the slot name. The
children of the slot node are added as children of the new slot instance. This
is useful if you wish to put patterns inside the slot. With the template::

  <html nevow:render="stuff"><nevow:slot name="slotName" /></html>

And the render method::

  def render_stuff(self, ctx, data):
      ctx.fillSlots('slotName', "Hello.")
      return ctx.tag

This document will be produced::

  <html>Hello.</html>

nevow:attr
----------

When the nevow:attr tag is encountered, the contents of the nevow:attr node will
be assigned to the attribute of the parent tag with the name of the value of the
name attribute. Perhaps an example will be a little clearer::

  <html><a><nevow:attr name="href">HELLO!</nevow:attr>Goodbye</a></html>

This document will be produced::

  <html><a href="HELLO!">Goodbye</a></html>

While this syntax is somewhat awkward, every other type of nevow tag and
attribute may be used inside the nevow:attr node. This makes setting attributes
of tags uniform with every other method of manipulating the XML template.

nevow:invisible
---------------

Sometimes you need to group some elements, because you need to use a
renderer for a group of children.

However, it may not be desirable to give these elements a parent/child
relationship in your XML structure.  For these cases, use nevow:invisible.

As suggested by the name, a nevow:invisible tag is removed in the rendered
XML. Here is an example::
 
  <html><nevow:invisible nevow:data="name" nevow:render="data" /></html>

With the data_name method::

  def data_name(self, ctx, data):
      return "Hello!"

Will result in the document::

 <html>Hello!</html>

xmlstr, htmlfile, and htmlstr
-----------------------------

xmlstr is a loader which is identical to xmlfile except it takes a string of XML
directly.

htmlfile and htmlstr should generally be avoided. They are similar to xmlfile
and xmlstr, except they use twisted.web.microdom in beExtremelyLenient mode to
attempt to parse badly-formed HTML (non-XHTML) templates. See the nevow.loaders
docstrings for more information.

Conclusions
===========

Nevow's xmlfile tag attribute language allows you to integrate
externally-designed XHTML templates into the Nevow rendering process.