However, if your web server is capable of recognising the user agent value and serving different content accordingly, you may be able to ensure that JSS style sheets are served only to requesting Netscape 4.0 browsers and that other browsers will be presented with CSS style sheets instead.
The main difference is in the notation used to describe the JSS rules.
There are two ways to call in a JSS defined style sheet, either with the <STYLE> tag, which embeds the style definitions into the page, or with the <LINK> tag, which includes them from an external document.
There are some special methods and functions defined for JSS to be used when creating styles. These are:
MSIE version 4.0 provides dynamic style control. It is improved significantly in version 5.0 and 5.5 and the same DOM based model is built into Netscape 6.0. The styles are available as host objects. You can modify the appearance of styled object in MSIE even after they have already been displayed. Changing the style or position of an object gives you all the capabilities that layers provided in Netscape, and an automatic damage repair redraw is also triggered if necessary when the style of an object is modified.
Netscape decided to make this interface available to the developer and exposed it as JSS. This means there is a conflicting alternative to CSS. It is very unlikely that JSS would be supported in any other browser than Netscape 4.0 given that most browser manufacturers are striving for standards compliance. They will all be supporting CSS2 fully in due course.
It is therefore recommended that while you may want to experiment with JSS, it is a deprecated item. As such you probably should avoid deploying it in any mission critical projects or using it in new developments.
The JSS functionality is removed from Netscape 6.0.