XForms

Improving the Web Forms Experience

Steven Pemberton

CWI and W3C
Kruislaan 413
1098 SJ Amsterdam
The Netherlands

Steven.Pemberton@cwi.nl
www.cwi.nl/~steven

About the Instructor

Steven Pemberton is a researcher at the CWI, The Centre for Mathematics and Computer Science, a nationally-funded research centre in Amsterdam, The Netherlands, the first non-military Internet site in Europe.

Steven's research is in interaction, and how the underlying software architecture can support the user. At the end of the 80's he built a style-sheet based hypertext system called Views.

Steven has been involved with the World Wide Web since the beginning. He organised two workshops at the first World Wide Web Conference in 1994, chaired the first W3C Style Sheets workshop, and the first W3C Internationalisation workshop. He was a member of the CSS Working Group from its start, and is a long-time member (now chair) of the HTML Working Group, and co-chair of the XForms Working Group. He is co-author of (amongst other things) HTML 4, CSS, XHTML and XForms.

Steven is also Editor-in-Chief of ACM/interactions.

Objectives

HTML Forms, introduced in 1993, were the basis of the e-commerce revolution. After 10 years experience, it has become clear how to improve on them, for the end user, the author, and the owners of the services that the forms are addressing. XForms is a new technology, announced in October 2003, intended to replace HTML Forms.

The advantages of XForms include:

The presenter is one of the authors of the XForms specifications, and is chair of the Forms Working Group that produced the technology.

This tutorial works from a basis of HTML Forms, and introduces XForms step-by-step. It covers essentially all of XForms except some technical details about events, and no more than a passing reference to the use of Schemas.

Emphasis is on how to improve the user experience, and how XForms improves accessibility and device independence, and makes the author’s life easy in producing a better experience.

Plan

HTML Forms: a great success!

Searching

Google

Buying

Amazon

Logging in

Yahoo

Configuring hardware

Linksys router

Reading mail

Reading mail

Composing email

Composing email

Etc etc

Problems with HTML Forms

Soundbite: "Javascript accounts for 90% of our headaches in complex forms, and is extremely brittle and unmaintainable."

XForms

The Approach

The essence is to separate what is being returned from how the values are filled in.

Advantages

... Advantages

... Advantages

... Advantages

Basic structure of XForms

Take this simple HTML form:

<html>
<head><title>Search</title></head>
<body>
    <form action="http://example.com/search"
          method="get">
         Find <input type="text" name="q">
         <input type="submit" value="Go">
    </form>
</body>
</html>

The main difference in XForms is that details of the values collected and how to submit them are gathered in the head, in an element called model; only the form controls are put in the body.

... basic structure

So in this case the minimum you need in the head is (XForms elements and attributes are in lower case):

<model>
   <submission
       action="http://example.com/search"
       method="get"
       id="s"/>
</model>

The <form> element is now no longer needed; the controls in the body look like this:

<input ref="q"><label>Find</label></input>
<submit submission="s">
    <label>Go</label>
</submit>

... basic structure

What you can hopefully work out from this is that form controls have a <label> element as child, the <input> uses "ref" instead of "name", and there is a separate submit control that links to the details of the submission in the head. So the complete example is:

Complete XForms search example

<h:html xmlns:h="http://www.w3.org/1999/xhtml"
        xmlns="http://www.w3.org/2002/xforms">
<h:head>
    <h:title>Search</h:title>
    <model>
        <submission
            action="http://example.com/search"
            method="get" id="s"/>
    </model>
</h:head>
<h:body>
  <h:p>
    <input ref="q"><label>Find</label></input>    <submit submission="s"><label>Go</label>
    </submit>
  </h:p>
</h:body></h:html>

Namespaces

HTML as default namespace

<html xmlns="http://www.w3.org/1999/xhtml"
      xmlns:f="http://www.w3.org/2002/xforms">
<head><title>Search</title>
  <f:model>
    <f:submission method="get" id="s"
        action="http://example.com/search"/>
  </f:model>
</head>
<body>
  <p><f:input ref="q">
       <f:label>Find</f:label>
     </f:input>     <f:submit submission="s">
        <f:label>Go</f:label>
     </f:submit>
  </p>
</body></html>

Choice of prefixes

Making XForms documents interoperable

<html xmlns="http://www.w3.org/1999/xhtml"
      xmlns:f="http://www.w3.org/2002/xforms">
<head>
   <object width="0" height="0" id="FormsPlayer"
     classid="CLSID:4D0ABA11-C5F0-4478-991A-375C4B648F58">
     <strong>FormsPlayer failed to load</strong>
   </object>
   <?import namespace="f"
            implementation="#FormsPlayer"?>

XForms equivalents for simple HTML Forms features

Now to compare one for one HTML forms controls with XForms equivalents

Simple Text Input

To input a single text element

First name: <input type="text" name="fname">

is written

<input ref="fname"><label>First name:</label>
</input>

There is no need to indicate that it is text: in the absence of any other information, by default it is text (called string in XForms).

input

We will see later how to give any control an initial value.

Textarea

To input multiline text

Message:
   <textarea name="message" rows="20" cols="80">
   </textarea>

is written

<textarea ref="message"><label>Message:</label>
</textarea>

textarea

Styling controls

Styling is done using a style sheet. For instance:

textarea[ref="message"]
    { font-family: sans-serif;
      height: 20em; width: 80em }

or

textarea[ref="message"]
    { font-family: serif;
      height: 2cm; width: 20% }

If you want all your textareas to have the same dimensions, you can use

textarea { font-family: sans-serif;
           height: 20em; width: 80em }

Adding a stylesheet

The easiest way to include a style sheet in your document is to add this at the beginning of the document:

<?xml version="1.0"?>
<?xml-stylesheet href="style.css"
                 type="text/css"?>

where 'style.css' is the name of your stylesheet, although in XHTML you can also say in the <head>:

<link rel="stylesheet" type="text/css"
    href="style.css"/>

(In IE you must do this)

Radio Buttons

Radio buttons select one value from a set:

Gender:
<input type="radio" name="sex" value="M"> Male
<input type="radio" name="sex" value="F"> Female

becomes

<select1 ref="sex">
   <label>Gender:</label>
   <item>
      <label>Male</label><value>M</value>
   </item>
   <item>
      <label>Female</label><value>F</value>
   </item>
</select1>

Presentation of controls

select1

select1 min

We will see later how to preselect a value.

Checkboxes

HTML Checkboxes select zero or more from a list.

Flavors:
<input type="checkbox" name="flavors" value="v"> Vanilla
<input type="checkbox" name="flavors" value="s"> Strawberry
<input type="checkbox" name="flavors" value="c"> Chocolate

is written

... checkboxes

<select ref="flavors" appearance="full">
   <label>Flavors:</label>
   <item>
      <label>Vanilla</label><value>v</value>
   </item>
   <item>
      <label>Strawberry</label><value>s</value>
   </item>
   <item>
      <label>Chocolate</label><value>c</value>
   </item>
</select>

select

Depending on the presence of the multiple attribute in HTML, menus select one, or zero or more from a list of options. You either use <select1> to select a single choice, or <select> to select zero or more.

Month:
<select multiple name="spring">
      <option value="Mar">March</option>
      <option value="Apr">April</option>
      <option>May</option>
</select>

would be written:

... menus

<select ref="spring" appearance="compact">
<label>Month:</label>
<item>
   <label>March</label><value>Mar</value>
</item>
<item>
    <label>April</label><value>Apr</value>
</item>
<item>
   <label>May</label><value>May</value>
</item>
</select>

select compact
If multiple isn't on the HTML select, use select1 instead.

Open and closed selections

You can add selection="open" on select and select1 to allow for open ended selections:

<select1 ref="color" selection="open">
<item><label>Red</label><value>red</value>
...

File Select

To select a file to be uploaded

<form method="post"
      enctype="multipart/form-data" ...>
 ...
File: <input type="file" name="attachment">

is written

<submission method="form-data-post" .../>
...
<upload ref="attachment">
   <label>File:</label>
</upload>

upload

Passwords

Password: <input type="password" name="pw">

is written

<secret ref="pw">
   <label>Password:</label>
</secret>

secret

Reset

<input type="reset">

is therefore written

<trigger>
   <label>Clear all fields</label>
   <reset ev:event="DOMActivate"/>
</trigger>

trigger

Buttons

Buttons have no predefined behavior, but have a behavior attached to them which is triggered when a relevant event occurs.

The button element

<input type="button" value="Show"
       onclick="show()">

can be written

<trigger><label>Show</label>
   <h:script ev:event="DOMActivate"
             type="text/javascript">show()
   </h:script>
</trigger>

or

... buttons

<trigger ev:event="DOMActivate"
         ev:handler="#show">
    <label>Show</label>
</trigger>

where "#show" locates the element (for instance a script element) that implements the behavior:

<script id="show" ...>...

XForms has a number of built in actions that can be executed by a button; see the reset button above for an example.

... buttons

The fact that the event attribute has a prefix, means that you have to add the following XML Namespace to the head:

xmlns:ev="http://www.w3.org/2001/xml-events"

We will be dealing more with events later.

Image Buttons

<input type="image" src="..." ...>

is written by putting an image into the <label> element:

<trigger...><label><h:img src="star.gif" .../>
</label></trigger>

or by specifying it in a stylesheet

<trigger id="activate" ...>

with a stylesheet rule

trigger#activate {
    background-image: url(button.png);
    background-repeat: none}

trigger with an image(Likewise for <submit>.)

Optgroup

Drink:
<select name="drink">
   <option selected value="none">None</option>
   <optgroup label="Soft drinks">
      <option value="h2o">Water</option>
      <option value="m">Milk</option>
      <option value="oj">Juice</option>
   </optgroup>
   <optgroup label="Wine and beer">
      <option value="rw">Red Wine</option>
      <option value="ww">White Wine</option>
      <option value="b">Beer</option>
   </optgroup>
</select>

is written

... optgroup

<select1 ref="drink">
   <label>Drink:</label>
   <item><label>None</label><value>none</value></item>
   <choices>
      <label>Soft drinks</label>
      <item><label>Water</label><value>h2o</value></item>
      <item><label>Milk</label><value>m</value></item>
      <item><label>Juice</label><value>oj</value></item>
   </choices>
   <choices>
      <label>Wine and beer</label>
      <item><label>Red wine</label><value>rw</value></item>
      <item><label>White wine</label><value>ww</value></item>
      <item><label>Beer</label><value>b</value></item>
   </choices>
</select1>

Grouping Controls

<fieldset>
   <legend>Personal Information</legend>
   Last Name: <input name="lastname" type="text">
   First Name: <input name="firstname" type="text">
   Address: <input name="address" type="text">
</fieldset>

is written

<group>
   <label>Personal Information</label>
   <input ref="lastname"><label>Last name:</label></input>
   <input ref="firstname"><label>First name:</label></input>
   <input ref="address"><label>Address:</label></input>
</group>

Note the consistent use of <label>.

Hidden Controls

As you will see shortly, there is no need for hidden controls in XForms.

Output Controls

XForms has two controls that are not in HTML, output and range.

The output control allows you to include values as text in the document.

Your current total is: <output ref="sum"/>

or

<output ref="sum"><label>Total</label></output>

This can be used to allow the user to preview values being submitted.

... output

You can also calculate values:

Total volume:
  <output value="height * width * depth"/>

(where height, width and depth are values collected by other controls.)

Range Controls

This control allows you to specify a constraint on a value.

<range ref="volume"
       start="1" end="10" step="0.5"/>

A user agent may represent this as a slider or similar.

Submitted Values

Making the Submitted Values Explicit

It is good practice to include an explicit instance, like this for the search example:

<model>
    <instance>
        <data xmlns=""><q/></data>
    </instance>
    <submission
        action="http://example.com/search"
        method="get" id="s"/>
</model>
...
<input ref="q">
   <label>Search</label>
</input>

... explicit values

Initial Values

For initialising controls including initialising checked boxes, and selected menu items etc., you just supply an instance with pre-filled values. For the search example:

<instance>
    <data xmlns=""><q>Keywords</q></data>
</instance>

would pre-fill the text control with the word Keywords.

... initial values for checkboxes

<select ref="flavors">
   <label>Flavors:</label>
   <item>
      <label>Vanilla</label><value>v</value>
   </item>
   <item>
      <label>Strawberry</label><value>s</value>
   </item>
   <item>
      <label>Chocolate</label><value>c</value>
   </item>
</select>

You can preselect vanilla and strawberry like this:

<instance>
  <data xmlns=""><flavors>v s</flavors></data>
</instance>

... initial values for menus

Similarly for the menus example, which looked like this:

<select ref="spring">
<label>Month:</label>
<item><label>March</label><value>Mar</value></item>
<item><label>April</label><value>Apr</value></item>
<item><label>May</label><value>May</value></item>
</select>

You can preselect March and April like this:

<instance>
  <data xmlns=""><spring>Mar Apr</spring></data>
</instance>

... initial values for choices

And for the optgroup example:

<select1 ref="drink">
   <label>Drink:</label>
   <item><label>None</label><value>none</value></item>
   <choices>
      <label>Soft drinks</label>
      <item><label>Water</label><value>h2o</value></item>
      <item><label>Milk</label><value>m</value></item>
      <item><label>Juice</label><value>oj</value></item>
   </choices>
   <choices>
      <label>Wine and beer</label>
      <item><label>Red wine</label><value>rw</value></item>
      <item><label>White wine</label><value>ww</value></item>
      <item><label>Beer</label><value>b</value></item>
   </choices>
</select1>

... choices

Preselect the value none like this:

<instance>
    <data xmlns=""><drink>none</drink></data>
</instance>

Hidden Values

<instance>
    <data xmlns="">
        <q/>
        <results>10</results>
    </data>
</instance>

Getting Initial Values From Elsewhere

'Editing' any XML document

... example

Editing example

Suppose a shop has very unpredictable opening hours (perhaps it depends on the weather), and they want to have a Web page that people can go to to see if it is open. Suppose the page in question has a single paragraph in the body:

<p>The shop is <strong>closed</strong> today.</p>

Well, rather than teaching the shop staff how to write HTML to update this, we can make a simple form to edit the page instead:

Editing XHTML page

<model>
   <instance
      src="http://www.example.com/shop.xhtml"/>
   <submission
      action="http://www.example.com/shop.xhtml"
      method="put" id="change"/>
</model
...
<select1 ref="/h:html/h:body/h:p/h:strong">
<label>The shop is now:</label>
<item><label>Open</label><value>open</value></item>
<item><label>Closed</label><value>closed</value></item>
</select1>
<submit submission="change"><label>OK</label></submit>

XPath

XPath selectors look like filename selectors

... XPath

Submitting

We shall now look at details of submission, like multiple submissions, submission methods, and what happens after submission.

Multiple Submissions

<model>
   <instance><data xmlns=""><q/></data></instance>
   <submission id="com"
       action="http://example.com/search"
       method="get"/>
   <submission id="org"
       action="http://example.org/search"
       method="get"/>
</model>

... multiple submissions

and then in the body:

<input ref="q"><label>Find:</label></input>
<submit submission="org">
    <label>Search example.org</label>
</submit>
<submit submission="com">
    <label>Search example.com</label>
</submit>

Find:

Submission Methods

HTML and XForms Equivalent Submission Methods
HTML XForms
method="get" method="get"
method="post"
enctype="application/x-www-form-urlencoded"		 method="urlencoded-post"
method="post"
enctype="multipart/form-data"		 method="form-data-post"

... submission methods

Life after Submit

... example of different submissions

... example

<model>
    <instance><data xmlns="">
        <accountnumber/><name/><address/>
    </data></instance>
    <submission method="get"
        action="http://example.com/prefill"
        id="prefill" replace="instance"/>
    <submission method="put"
        action="http://example.com/change"
        id="change" replace="none"/>
</model>
...
<input ref="accountnumber"><label>Account Number</label></input>
<submit submission="prefill"><label>Find</label></submit>
<input ref="name"><label>Name</label></input>
<textarea ref="address"><label>Address</label></textarea>
<submit submission="change"><label>Submit</label></submit>

Controlling Controls

Properties

The 'model binding' properties that you can control are:

... properties

Note that in XForms it is the collected value that has the property, not the control, but the property shows up on all controls bound to the value.

These properties use a <bind> element that goes in the <model>. To use bind, you must have an explicit <instance> element.

Disabled Controls = relevant

To disable controls you use the relevant property. For instance, to say that the credit card number only needs to be filled in if the person is paying by credit, you can write:

<model>
   <instance><data xmlns="">
      <amount/><method/><cc/><expires/>
   </data></instance>
   <bind nodeset="cc"
         relevant="../method='credit'"/>
   <bind nodeset="expires"
         relevant="../method='credit'"/>
</model>

... relevant

... relevant

... writing the controls

The controls could be written like this (but note that there is no indication that they may get disabled: that is inherited from the value they refer to):

<select1 ref="method">
   <label>Method of payment:</label>
   <item>
      <label>Cash</label>
      <value>cash</value>
   </item>
   <item>
      <label>Credit card</label>
      <value>credit</value>
   </item>
</select1>
<input ref="cc"><label>Card number:</label></input>
<input ref="expires"><label>Expiry date:</label></input>

... using structured instance values

If we used a structured instance, we could simplify this:

<model>
   <instance><data xmlns="">
      <amount/><method/>
      <cc>
        <number/><expires/>
      </cc>
   </data></instance>
   <bind nodeset="cc"
      relevant="../method='credit'"/>
</model>

and the controls then reference the children of 'cc':

<input ref="cc/number"><label>Card number:</label></input>
<input ref="cc/expires"><label>Expiry date:</label></input>

... using grouping on the controls

Instead of:

<input ref="cc/number"><label>Card number:</label></input>
<input ref="cc/expires"><label>Expiry date:</label></input>

grouping can be used to reset the context of the refs:

<group ref="cc">
   <input ref="number"><label>Card number:</label></input>
   <input ref="expires"><label>Expiry date:</label></input>
</group>

... works on buttons too

Although putting a ref on a trigger has no effect on the instance value being referred to, the relevance of the value can be used to affect the trigger:

<trigger ref="nextok">
   <label>Next</label>
   ...
</trigger>

Readonly Controls

Similarly to relevant, you can specify a condition under which a value is read-only. For instance:

<model>
   <instance><data xmlns="">
      <variant>basic</variant>
      <color>black</color>
   </data></instance>
   <bind nodeset="color"
         readonly="../variant='basic'"/>
</model>

This example says that the default value of color is black, and can't be changed if variant has the value basic.

Required Controls

A useful new feature in XForms is the ability to state that a value must be supplied before the form is submitted.

The simplest case is just to say that a value is always required. For instance, with the search example:

<model>
   <instance><data xmlns=""><q/></data></instance>
   <bind nodeset="q" required="true()"/>
   <submission .../>
</model>

... required

but like the readonly and relevant attributes, you can use any XPath expression to make a value conditionally required:

<bind nodeset="state"
      required="../country='USA'"/>

which says that the value for state is required when the value for country is "USA".

It is up to the browser to decide how to tell you that a value is required, but it may also allow you to define it in a stylesheet.

Constraint Property

This property allows you to add extra constraints to a value. For instance:

<bind nodeset="year" constraint=". &gt; 1970"/>

constrains the year to be after 1970.

Note the XPath use of "." to mean "this value".

">" has to be written as &gt; because of XML rules, but you should be used to that already.

Calculate Property

It is possible to indicate that a value in the instance is calculated from other values. For instance:

<bind ref="volume"
   calculate="../height * ../width * ../depth"/>

When a value is calculated like this, it automatically becomes readonly.

... calculate functions

There are a number of functions available, including:

Types

... types

... types

There are a number of useful built-in types you can use, including:

Combining Properties

If you have several binds referring to the same value, you can combine them:

<bind nodeset="q" type="xsd:integer"
                 required="true()"/>

More than one form in a document

... more than one form

<model id="search">
   <instance><data xmlns=""><q/></data></instance>
   <submission id="s" .../>
</model>
<model id="login">
   <instance><data xmlns=""><user/><passwd/></data></instance>
   <submission id="l" .../>
</model>
...
<input model="search" ref="q"><label>Find</label></input>
<submit submission="s"><label>Go</label></submit>
...
<input model="login" ref="user"><label>User name</label></input>
<secret model="login" ref="passwd"><label>Password</label></input>
<submit submission="l"><label>Log in</label></submit>

More than one instance in a model

... more than one instance

<model>
   <instance id="currencies">
      <currencies>
         <currency name="USD">125</currency>
         ...
   </instance>
   <instance id="costs">
      <item>
         <date/><amount/><currency/>
         ...
      </item>
   </instance>
</model>
...
<input ref="instance('costs')/date">
   <label>Date</date>
</input>

... more than one instance

<model>
   <instance id="tax" src="/finance/taxes"/>
   <instance>
      <employee xmlns="">
         <name/><number/>
         <salary/><taxrate/>
         ...
      </employee>
   </instance>

  <bind nodeset="taxrate"
    calculate="if(../salary &gt;
                  instance('tax')/limit,
                  50, 33)"/>

Using more than one instance

Useful for filling itemsets in select and select1:

<select ref="value">
   <label>...</label>
   <itemset nodeset="instance(x)">
    <label ref="names"/>
    <copy ref="values"/>
  </itemset>

or creating dynamic labels (think multilingual):

<label ref="instance(labels)/label[msg='age']"/>

<label> can also take src="..."

Bind instead of Ref

<model>
   <instance><data xmlns=""><q/></data></instance>
   <submission id="s" .../>
   <bind id="query" nodeset="q" required="true()"/>
</model>
...
<input bind="query"><label>Find</label></input>

Events

... HTML Events

Problems with HTML Events

XML Events

XML Events specifies the relationship between the event, observer and handler in a different way: (HTML example)

<input type="button">
   <script ev:event="DOMActivate"
           type="text/javascript">
      DoSomething();
   </script>
</input>

... an advantage

This approach allows you to specify handlers for different scripting languages: (HTML example)

<input type="button">
   <script ev:event="DOMActivate"
           type="text/javascript">
      ...
   </script>
   <script ev:event="DOMActivate"
           type="text/vbs">
      ...
   </script>
</input>

... another advantage

This approach allows you to specify handlers for different events: (HTML example)

<input type="button">
   <script ev:event="event1"
           type="text/javascript">
      ...
   </script>
   <script ev:event="event2"
           type="text/javascript">
      ...
   </script>
</input>

Actions

Other actions

... other actions

... other actions

Help, hint and alert

All forms controls have, as well as a <label> element, also <help>, <hint> and <alert>.

Events

There are very many events you can catch in XForms, including initialisation events, error notifications, values changing, validity changing, and submission done.

<submission id="save"
    action="file:results.xml"
    method="put"
    replace="none">
      <message ev:event="xforms-submit-done">
         Saved!
      </message>
</submission> 
...
<submit submission="save">
   <label>Save</label>
</submit>

Other ways to specify the event-observer-handler relationship

One way is to move the handler to some other part of the document, and specify the relationship there (like some variants of HTML use the for attribute on the <script> element):

 <action ev:observer="#button"
          ev:event="DOMActivate">
     ...
 </action>
...
<trigger id="button"/>

... another way

Another way is to move the handler somewhere, and specify the relationship in another place with the <listener> element:

<ev:listener observer="button"
             handler="dosomething"
             event="DOMActivate"/>
...
<action id="dosomething">...</action>
...
<trigger id="button"/>

... another way

And finally, you can specify the relationship on the observer itself:

<action id="dosomething">
      ...
</action>
...
<trigger ev:handler="dosomething"
         ev:event="DOMActivate"/>

Wizards: toggle and switch

These are used to reveal and hide parts of the interface.

<switch>
   <case id="inputname">
      <input ref="name">...</input>
      <trigger>
         <label>Next</label>
         <toggle case="inputage"
                 ev:event="DOMActivate" />
      </trigger>
   </case>
   <case id="inputage">
      <input ref="age">...</input>
      <trigger>...</trigger>
   </case>
   ...
</switch>

Repeat

Repeat allows you to bind to repeating items in an instance

<shoppinglist>
   <buy>eggs</buy>
   <buy>milk</buy>
   ...
</shoppinglist>
<repeat ref="buy" id="shoprepeat">
   <input ref="."><label>Buy</label></input>
</repeat>

A repeat sets the XPath context.

insert, delete, setfocus

You can use these with <repeat> to add and delete items, and to focus on a specific item.

<trigger>
   <label>Add</label>
   <insert ev:event="DOMActivate"
           nodeset="buy"
           at="index('shoprepeat')"
           position="after"/>
</trigger>
<trigger>
   <label>Delete</label>
   <delete ev:event="DOMActivate"
      nodeset="buy"
      at="index('shoprepeat')"/>
</trigger>

Implementations

"The age of the fat client is past" -- an implementor

The Future

Experience with XForms 1.0 has revealed a number of things:

A future iteration of XForms will address these issues.

More Information

The origin: www.w3.org/Markup/Forms, and if your company is a member: www.w3.org/Markup/Forms/Group

XForms: http://www.w3.org/TR/xforms/

XPath: http://www.w3.org/TR/xpath

XPath quick reference: http://www.mulberrytech.com/quickref/XSLTquickref.pdf

XML Events: http://www.w3.org/TR/xml-events/

validator: www.xformsinstitute.com