AH Formatter / XSL Formatter
Q&A

XSL Formatter uses an XSLT processor for converting XML documents and XSL stylesheets into XSL-FO, but XSL Formatter V3.1 reads XSL-FO for the speed-up of processing without the XSLT processor. Therefore, the encoding accepted with XSL Formatter is in the list described to the Online Manual. When other codes are used, the error message is output and processing stops. Please refer to 'Encodings' item in Overview of the Online Manual for details.

If you are using the "encoding" attribute of <xsl:output> element in Style Sheet, this value should be changed.