The <xsl:attribute-set> element creates a named set of attributes, which can then be applied as whole to the output document, in a manner similar to named styles in CSS.
<xsl:attribute-set name=NAME use-attribute-sets=LIST-OF-NAMES>
<xsl:attribute>
</xsl:attribute-set>nameSpecifies the name of the attribute set. The name must be a valid QName.
use-attribute-setsBuilds an attribute set from other attribute sets. The names of the contributing sets must be separated with whitespace characters and must not directly or indirectly embed themselves.
Top-level, must be the child of <xsl:stylesheet> or <xsl:transform>.
XSLT, section 7.1.4.
Supported.