The Extensible HyperText Markup Language (XHTML), is a markup language that has the same depth of expression as HTML, but also conforms to XML syntax.
A file is considered to be an XHTML document when the root element is
<html>.
There are a variety of default XHTML templates available when creating new documents from templates and they can be found in: .
The default templates for XHTML documents are located in the [OXYGEN_INSTALL_DIR]/frameworks/xhtml/templates/ folder.
The default CSS files used for rendering XHTML content in Author mode are stored in [OXYGEN_INSTALL_DIR]/frameworks/xhtml/css/.
By default, these default CSS files are merged with any that are specified in the document. For more information, see Configuring and Managing Multiple CSS Styles for a Framework.
Oxygen XML Author Eclipse plugin includes built-in transformation scenarios that allow you to transform XHTML documents to several types of DITA document types (topic, task, concept, reference). They can be found in the XHTML section in the Configure Transformation Scenario(s) dialog box.