[docbook-apps] From where the reference to CSS is added

[Sanjaya Liyanage]

hi dev,
    Currently the docbook is styled using CSS by applling directly to the
docbook XMLs.Once any user wrote his docbook document(XML) from where the
reference to the CSS(to driver.css in the trunk/css/xml/docbook) is being
added to that XML?

Thank you
Sanjaya