From:http://www.cnblogs.com/birdshome/archive/2005/01/03/85679.html
When we use the folder properties dialog box of Windows XP, we will find that in the Attributes category of the folder The Read-only and Hidden options are sometimes not in a completely checked or unchecked state, but are often in a state where they are checked but have a gray background. In fact, this kind of uncertain CheckBox status can also be expressed in the Web.
In a Web page, we can use to get a CheckBox control. The most common form of this control is checked (marked with a tick) or unchecked state. We can use mouse clicks to easily switch between these two states. We can also use scripting languages to change their states, such as using JavaScript scripts:
chkb.checked = true; or chkb.checked = false;
The following figure shows the three states that CheckBox can display:
The first and third are very common, and they It can be set using HTML, which means we can determine the initial state of the CheckBox through the attribute of an html element called checked. Although the Indeterminate state we are talking about here has been supported since IE4.0, there is no html element attribute to set its value. Instead, you can only use scripts to set its Indeterminate state.
For example, use JavaScript script (indeterminate defaults to false):
chkb.indeterminate = true; or chkb.indeterminate = false;
Note: CheckBox’s indeterminate is an independent The attribute has nothing to do with the checked and status values of CheckBox, which means that it will only affect the appearance of CheckBox. We can still use scripts to read the checked and status values normally.
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From:http://www.itbody.com/doc/Html/WEB/105537297.html
