(6) All-Purpose Elements

• HTML elements are supposed to convey structural semantics
  • lists [http://www.w3.org/TR/html4/struct/lists.html] are available in various flavors (ul, ol, dl)
  • various phrase markup elements [http://www.w3.org/TR/html4/struct/text.html#h-9.2.1] are available (em, strong, dfn, code, samp, kbd, var, cite, abbr, acronym)
  • various levels of headings [http://www.w3.org/TR/html4/struct/global.html#h-7.5.5] can be used (h1-h6)
• HTML content should represent structural information
  • not all content can be mapped to HTML elements
  • in many cases HTML elements are available (there are even diff elements [http://www.w3.org/TR/html4/struct/text.html#h-9.4])
• HTML also has all-purpose elements [http://www.w3.org/TR/html4/struct/global.html#h-7.5.4]
  • these elements have no semantics and are just containers
  • span is used as an inline container
  • div is used as a block container
  • all-purpose elements should only be used if no HTML element is available

(7) Retain Content Structures

• HTML should represent content structures
  • CSS can be used to tweak the formatting (if required)
• Rich content should be mapped to rich Web pages
  • use HTML elements if available
  • augment HTML elements with CSS classes [Cascading Style Sheets (CSS); Use Classes & Containers (1)] for more specific semantics
  • use Microformats [Semantic Web; Microformats (1)] for capturing more semantics
• HTML is just one possible representation of a resource
  • the data model of resources should not be limited by HTML
  • richer representations may become available in the future
  • why are there so few Web pages with tel: URIs?

(9) HTTP Web Services

• Services can be provided through URI/HTTP
  • URI-based services need input as a query string [Web Foundations (URI & HTTP); Query Information (1)]
  • the question is how the user gets information into the URI
• HTML forms provide an interface for assembling query strings
  • users fill out a form providing several fields
  • the browser submits the entered information by HTTP to a URI
  • the result of the request is displayed to the user
• HTTP has two different methods for submitting data
  • GET [Forms and GET (1)] encodes the data as a URI query string
  • POST [Forms and POST (1)] encodes the data as HTTP request entity

(10) Forms Mechanics

• HTML forms are normal Web pages (using form elements)
• The process receiving the form data produces a result page

(11) Forms Markup

• All form elements must be inside a form element
  • specifies the URI for submitting the form values (action="URI")
  • specifies the method for submitting the form values (method="GET [Forms and GET (1)]|POST [Forms and POST (1)]")
  • for POST forms, the encoding may be selected
• form contains regular HTML markup and form elements
  • the regular HTML markup creates the form's layout (table, list, texts)
  • the form elements create the controls for acquiring input data
• Each form should have a submit button
  • when pressing this button, the form values are sent to the action URI
  • without such a button, the form values cannot be submitted

(12) Forms Elements (User View)

• HTML provides a small set of form controls
• Sufficient for a many applications

(13) Forms Elements (Source View)

<form action="http://stevex.net/dump.php" method="POST" enctype="multipart/form-data"><table>

<tr><td>Text:</td><td><input type="text" name="text" value="text input"/></td></tr>

<tr><td>Password:</td><td><input type="password" name="password" value="hidden text"/></td></tr>

<tr><td>Checkbox:</td><td><input type="checkbox" name="check" value="1"/> <input type="checkbox" name="check" value="2"/> <input type="checkbox" name="check" value="3"/></td></tr>

<tr><td>Radio Button:</td><td><input type="radio" name="radio" value="1"/> <input type="radio" name="radio" value="2"/> <input type="radio" name="radio" value="3"/></td></tr>

<tr><td>Submit:</td><td><input name="submit" type="submit"/></td></tr>

<tr><td>File Upload:</td><td><input name="file" type="file"/></td></tr>

<tr><td>Text Areas:</td><td><textarea name="textarea" rows="2" cols="20"/></td></tr>

<tr><td>Selection:</td><td><select name="select"><option selected="selected">XML</option><option>SGML</option></select></td></tr>

<tr><td>Multiple Selection:</td><td><select name="mselect" multiple="multiple"><option>242</option><option>290-3</option><option>290-13</option></select>

</table></form>

(14) Forms and GET

• Limited to string-oriented form values
  • but HTML forms also allow file upload (this requires POST)
• All values of all form input fields are collected
  • for text and selection fields, this is one input field
  • for checkboxes and radio buttons, this collects the selected fields
• The browser composes a URI query string
  • the form submission is a set of name/value pairs (names may appear more than once!)
  • using URI query string notation, it is appended to the URI of the form's action
• GET is good!
  • URI-encoded queries can be bookmarked and otherwise reused (e.g., cached)
  • if possible, use GET when implementing a form

(15) Forms and POST

• GET encodes the values in the URI
  • for file uploads, this is not possible
  • HTTP's POST request method can upload data
• POST sends a request containing an entity
  • the HTTP request then looks similar to a response (header fields and entity)
  • the receiving process (the Web server) accepts the POST body
• Entities can use any format (it is specified in a header field)
  • just like e-mails, entities can have multiple parts
  • the parts are separated using the standard MIME mechanism

(16) POST Form Processing

• POST is used if the form specifies it
  • it can (but should not) be used for non-file forms
  • it should be used for file upload forms (otherwise, only the name is uploaded)
• File upload forms must specify the appropriate encoding
  • application/x-www-form-urlencoded is the default (values in the entity)
  • multipart/form-data is required for file upload (multipart form data)
• The server side must be prepared to receive POST requests
  • it must parse the entity rather than the URI's query string
  • form values can then be extracted from the entity
  • some environments (e.g., PHP) allow to handle GET/POST transparently

(17) Processing of Form Data

• Form data is always encoded
  • as a query string when using GET
  • in an encoded entity when using POST
  • in a multipart entity when using POST with multipart/form-data
• Parsing the form data should be done by existing software
  • most Web-aware programming environments provide this functionality
  • PHP allows access through different mechanisms

Query Parameter Test:
<?php
import_request_variables("gP", "form_");
echo $form_test;
?> 

(18) Structuring Forms

• HTML forms are very loosely structured
  • form somewhere representing the container
  • inside the form a random collection of HTML and form inputs
• Visually, the structure often is (and should be) easy to see
  • for non-visual access, more structure must be provided
  • accessibility has become a major issue on the Web
• Accessibility has many different facets
  • voice browsers must be able to read aloud Web forms
  • gateways should be able to intelligently re-structure Web forms

(19) Labels

• Label and form control are not connected by HTML

<tr><td>Text:</td><td><input type="text" name="text"/></td></tr>
<tr><td>Password:</td><td><input type="password" name="password"/></td></tr>

• The label element allows to make this connection
  • it connects a form control with the describing label
  • this association is now accessible to clients for processing

<tr>
  <td><label for="textctrl">Text:</label></td>
  <td><input type="text" name="text" id="textctrl"/></td>
</tr>
<tr>
  <td><label for="pwdctrl">Password:</label></td>
  <td><input type="password" name="password" id="pwdctrl"/></td>
</tr>

(20) Fieldsets

• Complex forms may need structuring
  • groups of controls for subsets of the collected data
  • this structure should be represented in markup

<fieldset><legend>Billing</legend>billing form controls …</fieldset>
<fieldset><legend>Shipping</legend> shipping form controls … </fieldset>

• Excellent example for HTML's markup design philosophy
  • if a client does not support fieldsets, the elements are ignored
  • the title of the fieldset will be displayed, because it is text

(21) Tabbing in Forms

• Tabbing is a very convenient way of navigating a form
  • after completing one field, users should be taken to the next
  • the order should be defined by the form creator, not by accident
• the tabindex attribute defines the tabbing order
  • it contains a number which is interpreted relative to other numbers
  • all form controls may carry a tabindex attribute
• tabindex 1-9: 1 7 3 6 8 2 1 4 5 9

(22) Disabled and Readonly Controls

• In complex scenarios, certain controls may be disabled or readonly
  • based on a workflow, some controls may not apply in all cases
  • for the sake of a consistent view, they should still be included in the interface
• Disabled controls are not used
  • they cannot be tabbed to and never receive focus
  • their value is not included in the form's submission data
• Readonly controls cannot be changed
  • they can be tabbed to and may receive focus
  • their value may not be changed (important for radio buttons and checkboxes!)
  • their value is included in the form's submission data
• Important: Never trust the Browser!

(23) Disabled and Readonly Controls Display

(25) XHTML and HTML

(26) Why XHTML?

• XHTML is XML and can be used with XML tools
• HTML is not XML and cannot be used with XML tools
• HTML very often is not validated
  • tag soup that is hard to work with (text-based processing)
  • much harder to process as a machine-readable resource
• Browsers behave differently for HTML and XHTML
  • backwards compatibility mode often is triggered by HTML
  • XHTML often triggers (more) standards-compliant behavior

(27) HTML → XHTML

• Element and attributes names are lowercase
• End tags are required
• Empty elements should use null end-tag syntax (with a space)
• Attribute values must always be quoted

<P>Paragraphs often are not closed properly.
<IMG WIDTH=200 HEIGHT=300 SRC="test.png">
<P>And images by definition are always empty elements.

<p>Paragraphs often are not closed properly.</p>
<img width="200" height="300" src="test.png" />
<p>And images by definition are always empty elements.</p>

(29) HTML Matters

• HTML is not just getting text displayed
• Good HTML allows better browsing
• First represent as much as possible in HTML
• Then add what is missing as CSS and/or microformats
• Graceful degradation is important