XSL 1.0 area-class trait "xsl-absolute" value semantics undefined

Nowhere in XSL 1.0 (or published errata) is the "xsl-absolute"
area-class trait value defined nor its purpose described.

Following are all instances of its appearance in the text:

4.2.5

"A reference-level-out-of-line area is an area with area-class
xsl-side-float or xsl-absolute;..."

6.1.1

"The values for this trait are: "xsl-normal", "xsl-absolute", ..."

6.4.5

"All areas generated by an fo:page-sequence have area-class
"xsl-absolute"."

6.4.13

"All areas generated by using the fo:region-body are of area-class
"xsl-absolute"."