Clarify and enhance \box tests

Author: brucemiller

t/digestion/box.pdf

@@ -1,25 +1,36 @@
 \documentclass{article}
 \def\testbox#1{%
- \ifvoid#1 Box #1 is empty
- \else\ifhbox#1 Box #1 is horizontal
- \else\ifvbox#1 Box #1 is vertical
+ \ifvoid#1 Box \string#1 is void
+ \else\ifhbox#1 Box \string#1 is horizontal
+ \else\ifvbox#1 Box \string#1 is vertical
  \fi\fi\fi
  \par}
 \begin{document}
-\setbox100=\hbox{Goodbye}
-\testbox{100}
-\setbox101=\hbox{Hello}
-\testbox{101}
-\setbox102=\vbox{\box101,\box100}
-\testbox{102}
-
-Using...
-\box102
-
-\setbox103=\hbox{}
-\testbox{103}
-
-\testbox{104}
+\newbox\myboxA
+\newbox\myboxB
+\newbox\myboxC
+Not yet set:\testbox{\myboxA}
+\setbox\myboxA=\hbox{}
+Set empty:\testbox{\myboxA}
+\setbox\myboxA=\hbox{Goodbye}
+\testbox{\myboxA}
+\setbox\myboxB=\hbox{Hello}
+\testbox{\myboxB}
+\setbox\myboxC=\vbox{\box\myboxB,\box\myboxA}
+\testbox{\myboxC}
+
+Combined: \box\myboxC
+And now: \testbox{\myboxA}.
+
+Curious unsetting behavior:
+\setbox\myboxA=\hbox{Once}
+Once? \box\myboxA \box\myboxA.
+
+\setbox\myboxA=\hbox{Once}
+Once? {\box\myboxA\box\myboxA}\box\myboxA\box\myboxA.
+
+\setbox\myboxA=\hbox{ and Again}
+Once? {\setbox\myboxA=\hbox{Once}\box\myboxA\box\myboxA}\box\myboxA\box\myboxA.
 
 \[ a + \hbox{a}\]
 \[ a + \vbox{a}\]

t/digestion/box.tex

@@ -5,28 +5,41 @@
   <resource src="LaTeXML.css" type="text/css"/>
   <resource src="ltx-article.css" type="text/css"/>
   <para xml:id="p1">
-    <p>Box 100 is horizontal</p>
+    <p>Not yet set: Box “myboxA is void</p>
   </para>
   <para xml:id="p2">
-    <p>Box 101 is horizontal</p>
+    <p>Set empty: Box “myboxA is horizontal</p>
   </para>
   <para xml:id="p3">
-    <p>Box 102 is vertical</p>
+    <p>Box “myboxA is horizontal</p>
   </para>
   <para xml:id="p4">
-    <p>Using…
-<inline-block vattach="bottom">
-        <p>Hello</p>
-        <p>,Goodbye</p>
-      </inline-block></p>
+    <p>Box “myboxB is horizontal</p>
   </para>
   <para xml:id="p5">
-    <p>Box 103 is horizontal</p>
+    <p>Box “myboxC is vertical</p>
   </para>
   <para xml:id="p6">
-    <p>Box 104 is empty</p>
+    <p>Combined: <inline-block vattach="bottom">
+        <p>Hello</p>
+        <p>,Goodbye</p>
+      </inline-block>And now:  Box “myboxA is void</p>
   </para>
   <para xml:id="p7">
+    <p>.</p>
+  </para>
+  <para xml:id="p8">
+    <p>Curious unsetting behavior:
+
+Once? Once.</p>
+  </para>
+  <para xml:id="p9">
+    <p>Once? Once.</p>
+  </para>
+  <para xml:id="p10">
+    <p>Once? Once and Again.</p>
+  </para>
+  <para xml:id="p11">
     <equation xml:id="S0.Ex1">
       <Math mode="display" tex="a+\hbox{a}" text="a + [a]" xml:id="S0.Ex1.m1">
         <XMath>
@@ -50,7 +63,7 @@
       </Math>
     </equation>
   </para>
-  <para xml:id="p8">
+  <para xml:id="p12">
     <equation xml:id="S0.Ex3">
       <Math mode="display" tex="a+\vbox{\hbox{a}\hbox{a}}" text="a + [aa]" xml:id="S0.Ex3.m1">
         <XMath>
@@ -80,7 +93,7 @@
       </Math>
     </equation>
   </para>
-  <para xml:id="p9">
+  <para xml:id="p13">
     <equation xml:id="S0.Ex5">
       <Math mode="display" tex="a-\lower 4.30554pt\vtop{\hbox{a}}" text="a - [a]" xml:id="S0.Ex5.m1">
         <XMath>
@@ -104,7 +117,7 @@
       </Math>
     </equation>
   </para>
-  <para xml:id="p10">
+  <para xml:id="p14">
     <equation xml:id="S0.Ex7">
       <Math mode="display" tex="a-\lower 4.30554pt\hbox{a}" text="a - [a]" xml:id="S0.Ex7.m1">
         <XMath>
@@ -117,7 +130,7 @@
       </Math>
     </equation>
   </para>
-  <para xml:id="p11">
+  <para xml:id="p15">
     <equation xml:id="S0.Ex8">
       <Math mode="display" tex="a-\lower 4.30554pt\hbox{a}" text="a - [a]" xml:id="S0.Ex8.m1">
         <XMath>