The sub text of a tooltip may contain markup. The markup is XML-based, and consists of a small subset of XHTML.
The following tags should be supported by the StatusNotifierHost visualization. Though it is optional, it is recommended. StatusNotifierHost that do not support these tags should filter them out.
Images can be used with absolute pathnames as image source. The alt tab is mandatory.
A full-blown HTML implementation is not required of this spec, and notifications should never take advantage of tags that are not listed above. As tooltips are not a substitute for complex dialogs, advanced layout is not necessary, and may in fact limit the number of systems where this system can run on, due to memory usage and screen space. Such examples are PDAs, certain cell phones, and slow PCs or laptops with little memory.
For the same reason, a full XML or XHTML implementation using XSLT or CSS stylesheets is not part of this specification. Information that must be presented in a more complex form should use an application-specific dialog, a web browser, or some other display mechanism.
The tags specified above mark up the content in a way that allows them to be stripped out on some implementations without impacting the actual content.