Function replace 

pub fn replace<N: DomNavigator>(
    _context: &mut DynamicContext<'_, N>,
    args: Vec<XPathValue<N>>,
) -> Result<XPathValue<N>, XPathError>

fn:replace($input as xs:string?, $pattern as xs:string, $replacement as xs:string, $flags as xs:string?) as xs:string

Replaces all occurrences of $pattern in $input with $replacement.

• FORX0001 if $flags contains invalid characters.
• FORX0002 if $pattern is not a valid regular expression.
• FORX0003 if $pattern matches a zero-length string.
• FORX0004 if $replacement has invalid syntax.