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 <select> tag gives you two, compact alternatives: pulldown menus and scrolling lists.

The <select> Tag

<option> tagged items inside the <select> tag of a form, you magically create a pull-down menu of choices.

<select>

• Function:
• Create single- and multiple-choice menus
• Attributes:
• MULTIPLE, NAME, and SIZE
• End tag:
• </select>; 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 <select> 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 <select> form data to the server.

The multiple attribute

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

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. If size is set to one and multiple is not specified, the <select> list is typically implemented as a pop-up menu, while values greater than one or specifying the multiple attribute cause the <select> 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? <select name=pets size=3 multiple >
<option>Dog <option>Cat <option>Bird <option>Fish </select> 

The result is shown in Figure 8-4, along with the change in appearance when the size attribute is set to one and multiple is not specified.

Figure 8-4: A <select> element, formatted with size=1 (left) and size=3 (right)

The <option> Tag

Use the <option> tag to define each item within a <select> form element.

<option>

• Function:
• Define available options within a <select> menu
• Attributes:
• SELECTED, and VALUE
• End tag:
• </option>; always omitted
• Contains:
• plain_text
• Used in:
• select_content

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

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 <option> tag.

As an example, consider these options:

<option value=Dog>Dog <option>Dog 

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

The selected attribute

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