The xhtml transformation generates XHTML output and a table of contents (TOC) file. This was the first transformation created for the DITA Open Toolkit, and originally served as the basis for all HTML-based transformations.
The XHTML output is always associated with the default DITA-OT CSS file (commonltr.css or commonrtl.css for right-to-left languages). You can use toolkit parameters to add a custom style sheet to override the default styles.
To run the XHTML transformation, set the transtype parameter to xhtml, or pass the --format=xhtml option to the dita command line.