diff --git a/xsl/pretext-assembly.xsl b/xsl/pretext-assembly.xsl
index 57ddcf46a7..5ba0cb3d7b 100644
--- a/xsl/pretext-assembly.xsl
+++ b/xsl/pretext-assembly.xsl
@@ -238,7 +238,7 @@ along with PreTeXt.  If not, see <http://www.gnu.org/licenses/>.
 
 <xsl:template match="node()|@*" mode="augment">
     <xsl:param name="parent-struct" select="''"/>
-    <xsl:param name="level" select="0"/>
+    <xsl:param name="level" select="-1"/>
     <xsl:param name="ordered-list-level" select="0"/>
 
     <xsl:copy>
@@ -1881,8 +1881,10 @@ along with PreTeXt.  If not, see <http://www.gnu.org/licenses/>.
 <!-- modal template will return a count of preceding peers at that level.   -->
 <!-- The @struct attribute is the structure number of the *parent*          -->
 <!-- (container), which seems odd here, but fits the general scheme better. -->
-<!-- The @level attribute is helpful, and trvislly to compute here.         -->
-<xsl:template match="part|chapter|appendix|section|subsection|subsubsection|exercises|solutions|reading-questions|references|glossary|worksheet" mode="augment">
+<!-- The @level attribute is helpful, and trivial to compute here.          -->
+<!-- Use &STRUCTURAL; here for easier maintenance, but some templates will  -->
+<!-- override with priority (e.g. frontmatter|backmatter)                   -->
+<xsl:template match="&STRUCTURAL;" mode="augment" priority="0">
     <xsl:param name="parent-struct"/>
     <xsl:param name="level"/>
     <xsl:param name="ordered-list-level" />
@@ -1945,7 +1947,7 @@ along with PreTeXt.  If not, see <http://www.gnu.org/licenses/>.
 <!-- backmatter.  So we need to increment the level in this case, only. -->
 <!-- NB: this might consolidate with above, but seems better solo.      -->
 <!-- NB: with some study and work, this situation might be improved?    -->
-<xsl:template match="frontmatter|backmatter" mode="augment">
+<xsl:template match="frontmatter|backmatter" mode="augment" priority="1">
     <xsl:param name="parent-struct"/>
     <xsl:param name="level"/>
 
diff --git a/xsl/pretext-common.xsl b/xsl/pretext-common.xsl
index 0ccf80aabb..9eb48658cb 100644
--- a/xsl/pretext-common.xsl
+++ b/xsl/pretext-common.xsl
@@ -525,37 +525,58 @@ Book (with parts), "section" at level 3
 <!-- use of levels computed during the "assembly" phase.  So we use careful  -->
 <!-- matches and we use careful choices for application.  At every           -->
 <!-- application we compute the "old" level to test for consistency.         -->
+<!-- 2024-12-19: next step - use "safe" version of level for now and watch   -->
+<!-- for issues. The safe version tests "new-level" for all uses of "level"  -->
 
 <!-- ####################################################################### -->
-<xsl:template match="part|chapter|appendix|section|subsection|subsubsection|exercises|solutions|reading-questions|references|glossary|worksheet" mode="new-level">
+<!-- temporary "level" entry point                                           -->
+<xsl:template match="&STRUCTURAL;" mode="level">
     <xsl:variable name="old-level">
-        <xsl:apply-templates select="." mode="level"/>
+        <xsl:apply-templates select="." mode="level-expensive"/>
     </xsl:variable>
-    <xsl:if test="not($old-level = @level)">
-        <xsl:message>PTX:BUG:  development bug, new level does not match old level for "<xsl:value-of select="local-name(.)"/>"</xsl:message>
+    <xsl:variable name="new-level">
+        <xsl:apply-templates select="." mode="new-level"/>
+    </xsl:variable>
+    <xsl:if test="not($old-level = $new-level)">
+        <xsl:message>PTX:BUG:  development bug, new level (<xsl:value-of select="$new-level"/>) does not match old level (<xsl:value-of select="$old-level"/>) for "<xsl:value-of select="local-name(.)"/>"</xsl:message>
         <xsl:apply-templates select="." mode="location-report" />
     </xsl:if>
-    <!-- actual value here, above is debugging -->
+    <!-- trust the old value -->
+    <xsl:value-of select="$old-level"/>
+</xsl:template>
+
+<!-- ####################################################################### -->
+<!-- These "new-level" eventually become "level"                             -->
+<xsl:template match="&STRUCTURAL;" mode="new-level">
     <xsl:value-of select="@level"/>
 </xsl:template>
 
-<xsl:template match="*" mode="new-level">
-    <xsl:message>PTX:BUG:   an element ("<xsl:value-of select="local-name(.)"/>") does not know its *new* level</xsl:message>
-    <xsl:apply-templates select="." mode="location-report" />
+<!-- Safety catch all -->
+<xsl:template match="*" mode="new-level" priority="-1">
+    <xsl:choose>
+        <xsl:when test="@level">
+            <xsl:message>PTX:BUG:   an element ("<xsl:value-of select="local-name(.)"/>") thinks it doesn't do *new* level but does </xsl:message>
+            <xsl:value-of select="@level"/>
+        </xsl:when>
+        <xsl:otherwise>
+            <xsl:message>PTX:BUG:   an element ("<xsl:value-of select="local-name(.)"/>") does not know its *new* level</xsl:message>
+            <xsl:apply-templates select="." mode="location-report" />
+        </xsl:otherwise>
+    </xsl:choose>
 </xsl:template>
 <!-- ####################################################################### -->
-
- <!-- Specific top-level divisions -->
+<!-- These "level-expensive" go away once there is confidence in "new-level" -->
+<!-- Specific top-level divisions -->
 <!-- article/frontmatter, article/backmatter are faux divisions, but   -->
 <!-- will function as a terminating condition in recursive count below -->
-<xsl:template match="book|article|slideshow|letter|memo|article/frontmatter|article/backmatter" mode="level">
+<xsl:template match="book|article|slideshow|letter|memo|article/frontmatter|article/backmatter" mode="level-expensive">
     <xsl:value-of select="0"/>
 </xsl:template>
 
 <!-- A book/part will divide the mainmatter, so a "chapter" is at -->
 <!-- level 2, so we also put the faux divisions at level 1 in the -->
 <!-- case of parts, to again terminate recursive count            -->
-<xsl:template match="book/part|book/frontmatter|book/backmatter" mode="level">
+<xsl:template match="book/part|book/frontmatter|book/backmatter" mode="level-expensive">
     <xsl:choose>
         <xsl:when test="$b-has-parts">
             <xsl:value-of select="1"/>
@@ -577,14 +598,14 @@ Book (with parts), "section" at level 3
 <!-- chapters of books, sections of articles, or in the case of         -->
 <!-- solutions or references, children of an appendix.                  -->
 
-<xsl:template match="colophon|biography|dedication|acknowledgement|preface|chapter|section|subsection|subsubsection|slide|appendix|index|colophon|exercises|reading-questions|references|solutions|glossary|worksheet" mode="level">
+<xsl:template match="colophon|biography|dedication|acknowledgement|preface|chapter|section|subsection|subsubsection|slide|appendix|index|colophon|exercises|reading-questions|references|solutions|glossary|worksheet" mode="level-expensive">
     <xsl:variable name="level-above">
-        <xsl:apply-templates select="parent::*" mode="level"/>
+        <xsl:apply-templates select="parent::*" mode="level-expensive"/>
     </xsl:variable>
     <xsl:value-of select="$level-above + 1"/>
 </xsl:template>
 
-<xsl:template match="*" mode="level">
+<xsl:template match="*" mode="level-expensive">
     <xsl:message>PTX:BUG:   an element ("<xsl:value-of select="local-name(.)"/>") does not know its level</xsl:message>
     <xsl:apply-templates select="." mode="location-report" />
 </xsl:template>
diff --git a/xsl/pretext-numbers.xsl b/xsl/pretext-numbers.xsl
index a471351b1e..adfd567f61 100644
--- a/xsl/pretext-numbers.xsl
+++ b/xsl/pretext-numbers.xsl
@@ -19,6 +19,11 @@ You should have received a copy of the GNU General Public License
 along with PreTeXt.  If not, see <http://www.gnu.org/licenses/>.
 *********************************************************************-->
 
+<!DOCTYPE xsl:stylesheet [
+    <!ENTITY % entities SYSTEM "entities.ent">
+    %entities;
+]>
+
 <xsl:stylesheet
     xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0"
     xmlns:xml="http://www.w3.org/XML/1998/namespace"
@@ -120,4 +125,17 @@ along with PreTeXt.  If not, see <http://www.gnu.org/licenses/>.
     <xsl:number from="backmatter" level="any" count="appendix|solutions" format="A"/>
 </xsl:template>
 
+<!-- "augment" may ask about any structural elements.  -->
+<!-- this is included as a low-priority catch-all for  -->
+<!-- anything not captured above.                      -->
+<xsl:template match="&STRUCTURAL;" mode="division-serial-number" priority="-1">
+    <xsl:value-of select="''"/>
+</xsl:template>
+
+<!-- final catch all to flag anything unexpected       -->
+<xsl:template match="*" mode="division-serial-number" priority="-1">
+    <xsl:message>PTX:BUG  the "division-serial-number" was applied to an element <xsl:value-of select="name(.)"/>. That is unexpected, please report it.</xsl:message>
+    <xsl:value-of select="''"/>
+</xsl:template>
+
 </xsl:stylesheet>