Each field will normally be given a distinct name. Several radio buttons can share the same name, as this is how you specify that they belong to the same control group - at any time, only one button in the group can be selected. In general, any field with a null value can be omitted from the contents list. Rather than extending the markup to support these features, HTML 3.0 provides a means for associating the form with a script. The user agent down-loads the script and interprets it locally.
Scripts handle a variety of messages for individual fields and the form as a whole.
When a field gains or loses the input focus Mouse clicks and drags over a field Keyboard events Scripts can examine and set properties of fields. They can also examine a small set of standard properties of the user agent, for instance the user's name, the time of day, the type of user agent, and so on. Scripts can't do anything that might jeopardize the user or the host machine. Scripts can't send messages over the network, or read or write files. The library calls that are allowed are restricted to a very small and well defined set.