Creating a custom message based in conditions witth ACL

I have a lot of XML files that are revised by random people.

These XML files can have the element PARA and these PARA can have a list of children.

When the PARA has a FOO child, it is expected that this FOO will be around spaces, for example:

<PARA>SOME PARA TEXT <FOO>SOME FOO TEXT</FOO> MORE PARA TEXT.</PARA>

But if there aren't spaces around, it would be ideal to show a message to the person who is reviewing the XML. This must happen for all PARA children.

Is there a way to do such a thing with ACL?