Hi
xsl:namespace-alias changes only the prefix instead of changing the namespace URI.
{xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSLT/Transfrom xmlns:out="out"}
  {xsl:namespace-alias stylesheet-prefix="out" result-prefix="xsl"/}
  {out:stylesheet version="1.0"}
    {out:template match="*"/}
  {/out:stylesheet}
{/xsl:stylesheet}

produces the following:
{xsl:stylesheet version="1.0"}
  {xsl:template match="*"/}
{/xsl:stylesheet}

according to the specification, the change of the prefix is optional,
but the namespace URI must be changed.
Therefore I'd expect the output look like follows:
{out:stylesheet version="1.0" xmlns:out="http://www.w3.org/1999/XSLT/Transform"}
  {out:template match="*"/}
{/out:stylesheet}

Regards,
Rudolf

PS: using build 59a