The following comments were received from Hans-Juergen Rennau:

in part 18.4.1 "Building an Expression Tree" I tiny text omissions (?) in the 
text - perhaps of interest to you. It is purely editorial.

handling xsl:sort
============
In the table, row "xsl:apply-templates instruction" there is:
"...; in addition, it has as children the select expression of the xsl:sort 
element, plus any expressions ..." [singular!]

I suspect this should be:
"...; in addition, it has as children the select expressions and/or contained 
sequence constructors of the xsl:sort elements, plus any expressions ..."

Similarly, in the row "xsl:perform-sort" it reads:
"The select expression or contained sequence constructor, together with any 
expressions that appear in attribute value templates ..."

but should perhaps be:
"The select expression or contained sequence constructor, together with the 
select expressions and/or contained sequence constructors of the xsl:sort 
elements, plus any expressions that appear in attribute value templates ..."

and in the row "xsl:for-each-group" it reads:
"...; in addition, it has as children any expression that appear in attribute 
value templates among the attribues of the xsl:sort elements..."

but should perhaps be the same text as in row "xsl:apply-templates", that is:
"...; in addition, it has as children the select expressions and/or contained 
sequence constructors of the xsl:sort elements, plus any expressions that appear 
in attribute value templates among the attributes of the xsl:sort elements..."

xsl:param, xsl:with-param: slight "inconsistencies" (correct, but may a little 
confuse)
=============================================================
Row "Template": ...; the xsl:param elements used to bind default values ..."
Row "xsl:iterate-instrcution": ...; the select expressions of all contained 
xsl:param elements

And the second variant is inferior, as it omits the possibility of a sequence 
constructor (in contrast to the first one, referring to "xsl:param", a row where 
we find "...the select attribute, or the contained sequence constructor".

---

Row "xsl:apply-templates": "... plus variable binding elements representing the 
xsl:with-param children"
Row "xsl:evaluate instruction": "... ; any child xsl:with-param elements"

Dealing with pattern
==============
Probably this is intentional and has a reason, but it strikes me that in 
"Template" the pattern is represented by a child e-node, whereas in 
"xsl:for-each-group instruction" the pattern is analyzed and then either not 
represented or represented by "preceding::*".

Kind regards,
-- Hans