HTML The Definitive Guide (107 page)

Chapter 10

Forms

10.7 Multiple Choice Elements

Checkboxes and radio buttons give you powerful means for creating multiple-choice questions and answers, but they can lead to long forms that are tedious to write and put a fair amount of clutter onscreen. The tag gives you two compact alternatives: pulldown menus and scrolling lists.

10.7.1 The

Tag

By placing a list of -tagged items inside the tag of a form, you magically create a pulldown menu of choices.

Function:

Create single-and multiple-choice menus

Attributes:

CLASS ONKEYPRESS

DIR ONKEYUP

DISABLED ONMOUSEDOWN

ID ONMOUSEMOVE

LANG ONMOUSEOUT

MULTIPLE ONMOUSEOVER

NAME ONMOUSEUP

ONBLUR ONSELECT

ONCHANGE SIZE

ONCLICK STYLE

ONDBLCLICK TABINDEX

ONFOCUS TITLE

ONKEYDOWN

End tag:

; never omitted

Contains:

select_content

Used in:

form_content

As with other form tags, the name attribute is required and used by the browser when submitting the choices to the server. Unlike radio buttons, however, no item is preselected, so if none is selected, no values are sent to the server when the form is submitted. Otherwise, the browser submits the selected item or collects multiple selections, each separated with commas, into a single parameter list and includes the name attribute when submitting form data to the server.

10.7.1.1 The multiple attribute

To allow more than one option selection at a time, add the multiple attribute to the tag. This causes the to behave like an element. If multiple is not specified, exactly one option can be selected at a time, just like a group of radio buttons.

10.7.1.2 The size attribute

The size attribute determines how many options are visible to the user at one time. The value of size should be a positive integer. The default value is 1 when size isn't specified. At size=1, if multiple is not specified, the browser typically displays the list as a pop-up menu.

Size values greater than one or specification of the multiple attribute cause the

to be displayed as a scrolling list.

In the following example, we've converted our previous checkbox example into a scrolling, multiple-choice menu. Notice also that the size attribute tells the browser to display three options at a time:

What pets do you own?

Dog

Cat

Bird

Fish

The result is shown in
Figure 10.5, along with the change in appearance when the
size attribute is set to 1 and multiple is not specified.

Figure 10.5: A element, formatted with size=1 (left) and size=3 (right)

10.7.2 The Tag

Use the

tag to define each item within a form control.

Function:

Define available options within a menu Attributes:

CLASS ONMOUSEDOWN

DIR ONMOUSEMOVE

DISABLED ONMOUSEOUT

ID ONMOUSEOVER

LABEL ONMOUSEUP

LANG ONSELECT

ONCLICK SELECTED

ONDBLCLICK STYLE

ONKEYDOWN TITLE

ONKEYPRESS VALUE

ONKEYUP

End tag:

; always omitted

Contains:

plain_text

Used in:

select_content

The browser displays the

tag's contents as an element within the tag's menu or scrolling list, so the content must be plain text only, without any other sort of markup.

10.7.2.1 The value attribute

Use the value attribute to set a value for each option the browser sends to the server if that option is selected by the user. If the value attribute has not been specified, the value of the option is set to the content of the tag.

As an example, consider these options:

Dog

Dog

Both have the same value. The first is explicitly set within the tag; the second defaults to the content of the tag itself.

10.7.2.2 The selected attribute

By default, all options within a multiple-choice tag are unselected. Include the selected attribute (no value) inside the tag to preselect one or more options, which the user may then deselect. Single-choice tags will preselect the first option if no option is explicitly preselected.

10.7.2.3 The label attribute

Normally, the contents of the tag are used to create the label for that element when it is displayed to the user. If the label attribute is supplied, its value is used as a label instead.

10.7.3 The Tag

Menus of choices in forms can be quite large, making them difficult to display and use. In these cases, it is helpful to group related choices, which can then be presented as a set of nested, cascading menus to the user. New in HTML 4.0, the tag brings this capability to HTML forms, albeit limited.

Function:

Group related elements within a menu Attributes:

CLASS ONKEYUP

DIR ONMOUSEDOWN

DISABLED ONMOUSEMOVE

ID ONMOUSEOUT

LABEL ONMOUSEOVER

LANG ONMOUSEUP

ONCLICK ONSELECT

ONDBLCLICK STYLE

ONKEYDOWN TITLE

ONKEYPRESS

End tag:

; may be omitted

Contains:

optgroup_contents

Used in:

select_content

Use the

tag only within a tag, and it may only contain tags.

The browser creates submenus for each tag within the main menu. For example, you might use to present a form menu of states organized by region:

Maine

New Hampshire

...

Georgia

Florida

...

...

Since no browser yet supports the tag, we can't show you what this menu might look like. However, it will probably look and feel much like the familiar pulldown menus that are a common feature of most graphical user interfaces. When selected with the mouse or keyboard, the optgroup probably will open into one or more menus. For instance, our "state" example probably will have submenus labeled "Northeast," "South," and so on, each of which can be pulled open to reveal a list of included states.

Regrettably, the biggest drawback to the tag is that it cannot be nested, limiting you to one level of submenus. Presumably this restriction will be lifted in a future version of HTML.

10.7.3.1 The label attribute

Use the label attribute to define an optgroup's submenu title to the user. You should keep the label

short and to the point, to ensure that the menu can be displayed easily on a large variety of displays.

10.6 Multiline Text Areas

10.8 General Form Control

Attributes