@pedroigor  look for other usages of relative-to in jboss-as-config-x.x.xsd. It normally comes in two parts
* file - which maybe should be 'dir' in your case
* relative-to

The way these work is that if 'relative-to' is not specified, 'file' is taken as an absolute path. If 'relative-to' is specified, it is taken to be the name of a path from the '<paths>' section and 'file' is relative to that path.

e.g.
<... file="/some/where/a/file"> (absolute)
<.... file="thing" relative-to="some.path.from.the.paths.section">

Also look for usages of PathManagerService in some of the subsystems. It is used to resolve these values into something real