Fix \hphantom width (#1809)

* Fix \hphantom width

* Spin up phony screenshot test

* Make better choice of smash screenshot test

* Real screenshotter test

* Add strict mode

* Fix lint error

* useStrictBehavior

* Revert to previous strict setting

* useStrictBehavior "phantomSpacing"

* Fix tests via nonstrictSettings

* Fix documentation

* Remove bin|rel

src/functions/phantom.js

@@ -71,7 +71,8 @@ defineFunction({
             children: [{type: "elem", elem: node}],
         }, options);
 
-        return node;
+        // For spacing, TeX treats \smash as a math group (same spacing as ord).
+        return buildCommon.makeSpan(["mord"], [node], options);
     },
     mathmlBuilder: (group, options) => {
         const inner = mml.buildExpression(ordargument(group.body), options);

src/functions/smash.js

@@ -55,7 +55,7 @@ defineFunction({
     },
     htmlBuilder: (group, options) => {
         const node = buildCommon.makeSpan(
-            ["mord"], [html.buildGroup(group.body, options)]);
+            [], [html.buildGroup(group.body, options)]);
 
         if (!group.smashHeight && !group.smashDepth) {
             return node;
@@ -85,10 +85,13 @@ defineFunction({
         // makeVList applies "display: table-cell", which prevents the browser
         // from acting on that line height. So we'll call makeVList now.
 
-        return buildCommon.makeVList({
+        const smashedNode = buildCommon.makeVList({
             positionType: "firstBaseline",
             children: [{type: "elem", elem: node}],
         }, options);
+
+        // For spacing, TeX treats \hphantom as a math group (same spacing as ord).
+        return buildCommon.makeSpan(["mord"], [smashedNode], options);
     },
     mathmlBuilder: (group, options) => {
         const node = new mathMLTree.MathNode(