The attribute regroot is not documented on https://izpack.atlassian.net/wiki/display/IZPACK/Dynamic+Variables.
Because it seems to be not functional at the moment, the documentation should be delayed until feature does work. See
From the analysis it seems that regroot is no longer needed, it was used previously when reg query command was ran (there you have to specify separate root and key), now it seems that you do not need that at all, for registry values commands reg export to get the key and reg import to create the key are ran. They either require absolute path and/or registry file respectively.
So I would suggest to get rid of the regroot attribute completely.
Also another note, when I used double backslashes in regkey attribute it could not get the key for me though it is described so in the documentation.
Personally I'd agree to remove the meaning less attribute regroot from XSD and its processing from the code.
This attribute has been probably forgotten after the migration to reg export. From my remembering, the change from reg query to reg export has been done for the reason of getting the proper encoding (the registry is encoded in UTF-16). This change can't be even found in the Git history (has been merged from the original ini4j project).
Candidate for the next bug fix release after 5.1.0.
Thanks for this contribution.