Outputs the ID of the theme currently applied to the website in context. The identifier is modified such that underscores are changed to dashes.
Use a value of 1 to prevent underscores from being automatically converted to dashes. This modifier was added to Movable Type 6.0.4.
One use for this is to output the WebsiteThemeID as the HTML “body” ID to make targetting for styling easier:
<body id="<mt:WebsiteThemeID>"> ... </body>