Drupal 7 Module Development

Building an Admin Interface
Each element is keyed by a unique string, which will become the element's name
attribute when the form is rendered. This element is then assigned an array
of attributes.
For a complete matrix of all the form elements defined by Drupal as well
as the properties each one implements, visit:
http://api.drupal.org/api/drupal/developer--topics--
forms_api_reference.html/7
'#type' => 'textfield',
The first attribute is '#type' which defines what form element will be rendered.
All the standard HTML form elements have types, as well as some Drupal-specific
elements defined. In this case we are creating a basic textfield.
'#title' => t('Warning e-mail subject'),
'#description' => t(
'The subject of the e-mail which will be sent to users.'),
The next two attributes, '#title' and '#description' define the element's label
and an optional description.
Any attribute that a standard HTML element has are available as Form API
properties or attributes as well. For instance, see the following two lines of code.
'#size' => 40,
'#maxlength' => 120,
As you would expect, these define the size and maxlength attributes of our text field.
One of the nice things about Form API is that it will automatically validate many of
the element's attributes when the form is submitted. In this case Drupal will throw
an error if any text is submitted with a length greater than the element's maxlength.
All this happens transparently with no extra code from the developer.
Form API also adds some convenience properties for validation purposes,
like '#required'.
'#required' => TRUE,
When '#required' is set to TRUE, Drupal will throw an error if the form is submitted
without a value in that element. Required fields are also marked with an asterisk in
their labels. Again, this happens transparently without any extra code. Drupal will
even highlight the field when an error applies to it! This on-the-fly error handling and
form validation is one of the reasons Form API is such a boon to developers. It really
reduces the amount of drudgery involved in creating and handling HTML forms.
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