dbxml:contains($toLookIn as xs:string?, $toLookFor as xs:string?) as xs:boolean

This function behaves identically to fn:contains() in the XQuery 1.0 and XPath 2.0 Functions and Operators Specification except that it operates in a case- and diacritic-insensitive manner. This allows case-insensitive queries that can be optimized by Berkeley DB XML substring indices.