The HotZone plugin gives you Information about the tiddler currently in focus.

Everytime a tiddler's body reaches a defined threshold, the value of $:/temp/focussedTiddler is updated with the title of the currently focussed tiddler. Moreover, a css class (hzone-focus) is added to the tiddler frame to allow css styling.

You could write a small widget that listens to the changes of $:/temp/focussedTiddler to

• Unfold the table of contents or highlight the current topic.
• Change the page title
• Update the permalink in the address bar
• Log the user behavior
• Highlight the focussed tiddler

TiddlyMap uses the HotZone plugin to update its live view in the sidebar. Now that's cool or not?

You can use this plugin by importing it (e.g. from the TiddlyMap demo site). Configure the plugin by opening TiddlyWiki's configuration and selecting HotZone in the plugin section.