Historically, HTML pages have often been created with little concern for correct, computer-readable syntax, and browsers have been perhaps too forgiving. With the advent of XML, however, such loose standards have lost their appeal. XHTML takes the usability of HTML and weaves it in with the strict, precise nature of XML.

XHTML and INDI

INDI utilizes XHTML which can be validated against the xhtml1-transitional.dtd published by the W3C (World Wide Web Consortium).