You can see that the node test node() is true for  attribute nodes if
you apply it to an axis that has such nodes, as in:

attribute:node()

To further clarify or mystify or nodify all this node salad, here's an
alternative, more symmetrical syntax for our beloved identity template:

  <xsl:template match="@node()|node()">
    <xsl:copy>
      <xsl:apply-templates select="@node()|node()"/>
    </xsl:copy>
  </xsl:template>

Interestingly (and regrettably), LibXSLT 1.1.24 will compile this in the
path expression (@select), but not in the match pattern.

node() matches attributes in other contexts too, such as the xpath2
expression

@foo instance of node()