Write log file during xslt and xmlvalidate

Hello,

I have implemented a migration process in Ant with xsl transformations
and XML Schema validations. I want to write the errors/warnings during
validation and xsl:messages during  into a log file.

I know there is the echo task which can write to a file, but it is only
able to write from the built script and not from the task. There must be
a way to pass task output to a log file.

Has anybody done this before?

Thanks Robert