code: public void setAttribute(String name, String value, String facet)
              throws JspException
      {
          if (facet != null) {
              String s = Bundle.getString("Tags_AttributeFacetNotSupported", new Object[]{facet});
              registerTagError(s, null);
          }
          AbstractHtmlState tsh = getState();
          setStateAttribute(name, value, tsh);
      }
docs: Base support for the <code>attribute</code> tag.  This requires that the tag buffer their body and
  write attribute in the end tag.  For the HTML tags it is not legal to set
  the <code>id</code> or <code>name</code> attributes.  In addition, the base tag does
  not allow facets to be set.  If the attribute is legal it will be added to the
  general expression map stored in the <code>AbstractHtmlState</code> of the tag.
  @param name  The name of the attribute.  This value may not be null or the empty string.
  @param value The value of the attribute.  This may contain an expression.
  @param facet The name of a facet to which the attribute will be applied.  This is optional.
  @throws JspException A JspException may be thrown if there is an error setting the attribute.