feat: Support \vcenter and \hbox (#2452)

* Support \vcenter, \raise, \lower, and \hbox

* Update screenshots

* Edit docs for strict and hbox to

* Fix typo for \hbox to

* Update Safari screenshot

* Augment docs for \vcentcolon

* Edit vcenter MathML comment.

* Remove pointless class from vcenter MathML

* Withdraw \raise and \lower

* Updatae Chrome and Firefox screenshots

* Update Safari screenshot

* Delete allowedInArgument setting

Co-authored-by: ylemkimon <y@ylem.kim>

* Update Chrome and Firefox screenshots

* Update Chrome and Firefox screenshots take 2

* Update screenshot

Co-authored-by: ylemkimon <y@ylem.kim>

contrib/render-a11y-string/render-a11y-string.js

@@ -327,6 +327,11 @@ const handleObject = (
             break;
         }
 
+        case "hbox": {
+            buildA11yStrings(tree.body, a11yStrings, atomType);
+            break;
+        }
+
         case "kern": {
             // No op: we don't attempt to present kerning information
             // to the screen reader.
@@ -546,6 +551,11 @@ const handleObject = (
                 `KaTeX-a11y: enclose node with ${tree.label} not supported yet`);
         }
 
+        case "vcenter": {
+            buildA11yStrings(tree.body, a11yStrings, atomType);
+            break;
+        }
+
         case "vphantom": {
             throw new Error("KaTeX-a11y: vphantom not implemented yet");
         }

contrib/render-a11y-string/test/render-a11y-string-spec.js

@@ -272,6 +272,13 @@ describe("renderA11yString", () => {
         });
     });
 
+    describe("hbox", () => {
+        test("\\hbox", () => {
+            const result = renderA11yString("x+\\hbox{y}");
+            expect(result).toMatchInlineSnapshot(`"x, plus, y"`);
+        });
+    });
+
     describe("inner", () => {
         test("\\ldots", () => {
             const result = renderA11yString("\\ldots");
@@ -524,6 +531,13 @@ describe("renderA11yString", () => {
         });
     });
 
+    describe("vcenter", () => {
+        test("\\vcenter", () => {
+            const result = renderA11yString("x+\\vcenter{y}");
+            expect(result).toMatchInlineSnapshot(`"x, plus, y"`);
+        });
+    });
+
     describe("verb", () => {
         test("\\verb", () => {
             const result = renderA11yString("\\verb|hello|");

docs/support_table.md

@@ -456,7 +456,8 @@ use `\ce` instead|
 |\harr|$\harr$||
 |\hat|$\hat{\theta}$|`\hat{\theta}`|
 |\hbar|$\hbar$||
-|\hbox|<span style="color:firebrick;">Not supported</span>||
+|\hbox|$\hbox{$x^2$}$|`\hbox{$x^2$}`|
+|\hbox to <dimen>| <span style="color:firebrick;">Not supported</span> ||
 |\hdashline|$\begin{matrix}a&b\\ \hdashline c &d\end{matrix}$|`\begin{matrix}`<br>&nbsp;&nbsp;&nbsp;`a & b \\`<br>&nbsp;&nbsp;&nbsp;`\hdashline`<br>&nbsp;&nbsp;&nbsp;`c & d`<br>`\end{matrix}`|
 |\hearts|$\hearts$||
 |\heartsuit|$\heartsuit$||
@@ -865,7 +866,7 @@ use `\ce` instead|
 |\R|$\R$||
 |\r|$\text{\r{a}}$|`\text{\r{a}}`|
 |\raise|<span style="color:firebrick;">Not supported</span>|see `\raisebox`|
-|\raisebox|$h\raisebox{2pt}{ighe}r$|`h\raisebox{2pt}{ighe}r`|
+|\raisebox|$h\raisebox{2pt}{ighe}r$|`h\raisebox{2pt}{$ighe$}r`|
 |\rang|$\langle A\rang$|`\langle A\rang`|
 |\rangle|$\langle A\rangle$|`\langle A\rangle`|
 |\Rarr|$\Rarr$||
@@ -1176,8 +1177,9 @@ use `\ce` instead|
 |\vartriangleright|$\vartriangleright$||
 |\varUpsilon|$\varUpsilon$||
 |\varXi|$\varXi$||
-|\vcentcolon|$\vcentcolon$||
-|\vcenter|<span style="color:firebrick;">Not supported</span>||
+|\vcentcolon|$\mathrel{\vcentcolon =}$|`\mathrel{\vcentcolon =}`|
+|\vcenter|$a+\left(\vcenter{\frac{\frac a b}c}\right)$|`a+\left(\vcenter{\hbox{$\frac{\frac a b}c$}}\right)`<br>TeX (strict) syntax|
+|\vcenter|$a+\left(\vcenter{\frac{\frac a b}c}\right)$|`a+\left(\vcenter{\frac{\frac a b}c}\right)`<br>non-strict syntax|
 |\Vdash|$\Vdash$||
 |\vDash|$\vDash$||
 |\vdash|$\vdash$||

docs/supported.md

@@ -236,11 +236,14 @@ In display math, KaTeX does not insert automatic line breaks. It ignores display
 
 ||||
 |:--------------|:----------------------------------------|:-----
-|$x_n$ `x_n` |$\stackrel{!}{=}$ `\stackrel{!}{=}`  |$a \atop b$ `a \atop b`
-|$e^x$ `e^x` |$\overset{!}{=}$ `\overset{!}{=}` |$a\raisebox{0.25em}{b}c$ `a\raisebox{0.25em}{b}c`
-|$_u^o $ `_u^o `|$\underset{!}{=}$ `\underset{!}{=}` | $$\sum_{\substack{0<i<m\\0<j<n}}$$ `\sum_{\substack{0<i<m\\0<j<n}}`
+|$x_n$ `x_n` |$\stackrel{!}{=}$ `\stackrel{!}{=}`| $a \atop b$ `a \atop b`
+|$e^x$ `e^x` |$\overset{!}{=}$ `\overset{!}{=}`  | $a\raisebox{0.25em}{$b$}c$ `a\raisebox{0.25em}{$b$}c`
+|$_u^o $ `_u^o `| $\underset{!}{=}$ `\underset{!}{=}` | $a+\left(\vcenter{\frac{\frac a b}c}\right)$ `a+\left(\vcenter{\hbox{$\frac{\frac a b}c$}}\right)`
+||| $$\sum_{\substack{0<i<m\\0<j<n}}$$ `\sum_{\substack{0<i<m\\0<j<n}}`
 
-The second argument of `\raisebox` can contain math if it is nested within `$…$` delimiters, as in `\raisebox{0.25em}{$\frac a b$}`
+`\raisebox` and `\hbox` put their argument into text mode. To raise math, nest `$…$` delimiters inside the argument as shown above. 
+
+`\vcenter` can be written without an `\hbox` if the `strict` rendering option is *false*. In that case, omit the nested `$…$` delimiters.
 
 ### Overlap and Spacing
 

src/functions.js

@@ -21,6 +21,7 @@ import "./functions/font";
 import "./functions/genfrac";
 import "./functions/horizBrace";
 import "./functions/href";
+import "./functions/hbox";
 import "./functions/html";
 import "./functions/htmlmathml";
 import "./functions/includegraphics";
@@ -47,4 +48,5 @@ import "./functions/symbolsSpacing";
 import "./functions/tag";
 import "./functions/text";
 import "./functions/underline";
+import "./functions/vcenter";
 import "./functions/verb";

src/functions/hbox.js

@@ -0,0 +1,39 @@
+// @flow
+import defineFunction, {ordargument} from "../defineFunction";
+import buildCommon from "../buildCommon";
+import mathMLTree from "../mathMLTree";
+
+import * as html from "../buildHTML";
+import * as mml from "../buildMathML";
+
+// \hbox is provided for compatibility with LaTeX \vcenter.
+// In LaTeX, \vcenter can act only on a box, as in
+// \vcenter{\hbox{$\frac{a+b}{\dfrac{c}{d}}$}}
+// This function by itself doesn't do anything but prevent a soft line break.
+
+defineFunction({
+    type: "hbox",
+    names: ["\\hbox"],
+    props: {
+        numArgs: 1,
+        argTypes: ["text"],
+        allowedInText: true,
+        primitive: true,
+    },
+    handler({parser}, args) {
+        return {
+            type: "hbox",
+            mode: parser.mode,
+            body: ordargument(args[0]),
+        };
+    },
+    htmlBuilder(group, options) {
+        const elements = html.buildExpression(group.body, options, false);
+        return buildCommon.makeFragment(elements);
+    },
+    mathmlBuilder(group, options) {
+        return new mathMLTree.MathNode(
+          "mrow", mml.buildExpression(group.body, options)
+        );
+    },
+});

src/functions/raisebox.js

@@ -44,4 +44,3 @@ defineFunction({
         return node;
     },
 });
-

src/functions/vcenter.js

@@ -0,0 +1,44 @@
+// @flow
+import defineFunction from "../defineFunction";
+import buildCommon from "../buildCommon";
+import mathMLTree from "../mathMLTree";
+
+import * as html from "../buildHTML";
+import * as mml from "../buildMathML";
+
+// \vcenter:  Vertically center the argument group on the math axis.
+
+defineFunction({
+    type: "vcenter",
+    names: ["\\vcenter"],
+    props: {
+        numArgs: 1,
+        argTypes: ["original"], // In LaTeX, \vcenter can act only on a box.
+        allowedInText: false,
+    },
+    handler({parser}, args) {
+        return {
+            type: "vcenter",
+            mode: parser.mode,
+            body: args[0],
+        };
+    },
+    htmlBuilder(group, options) {
+        const body = html.buildGroup(group.body, options);
+        const axisHeight = options.fontMetrics().axisHeight;
+        const dy = 0.5 * ((body.height - axisHeight) - (body.depth + axisHeight));
+        return buildCommon.makeVList({
+            positionType: "shift",
+            positionData: dy,
+            children: [{type: "elem", elem: body}],
+        }, options);
+    },
+    mathmlBuilder(group, options) {
+        // There is no way to do this in MathML.
+        // Write a class as a breadcrumb in case some post-processor wants
+        // to perform a vcenter adjustment.
+        return new mathMLTree.MathNode(
+            "mpadded", [mml.buildGroup(group.body, options)], ["vcenter"]);
+    },
+});
+

src/parseNode.js

@@ -256,6 +256,12 @@ type ParseNodeTypes = {
         size: StyleStr | "auto",
         barSize: Measurement | null,
     |},
+    "hbox": {|
+        type: "hbox",
+        mode: Mode,
+        loc?: ?SourceLocation,
+        body: AnyParseNode[],
+    |},
     "horizBrace": {|
         type: "horizBrace",
         mode: Mode,
@@ -436,6 +442,12 @@ type ParseNodeTypes = {
         loc?: ?SourceLocation,
         body: AnyParseNode,
     |},
+    "vcenter": {|
+        type: "vcenter",
+        mode: Mode,
+        loc?: ?SourceLocation,
+        body: AnyParseNode,
+    |},
     "xArrow": {|
         type: "xArrow",
         mode: Mode,

test/katex-spec.js

@@ -1642,6 +1642,36 @@ describe("A \\pmb builder", function() {
     });
 });
 
+describe("A raise parser", function() {
+    it("should parse and build text in \\raisebox", function() {
+        expect("\\raisebox{5pt}{text}").toBuild(strictSettings);
+        expect("\\raisebox{-5pt}{text}").toBuild(strictSettings);
+    });
+
+    it("should parse and build math in non-strict \\vcenter", function() {
+        expect("\\vcenter{\\frac a b}").toBuild(nonstrictSettings);
+    });
+
+    it("should fail to parse math in \\raisebox", function() {
+        expect("\\raisebox{5pt}{\\frac a b}").not.toParse(nonstrictSettings);
+        expect("\\raisebox{-5pt}{\\frac a b}").not.toParse(nonstrictSettings);
+    });
+
+    it("should fail to parse math in an \\hbox", function() {
+        expect("\\hbox{\\frac a b}").not.toParse(nonstrictSettings);
+    });
+
+    it("should fail to build, given an unbraced length", function() {
+        expect("\\raisebox5pt{text}").not.toBuild(strictSettings);
+        expect("\\raisebox-5pt{text}").not.toBuild(strictSettings);
+    });
+
+
+    it("should build math in an hbox when math mode is set", function() {
+        expect("a + \\vcenter{\\hbox{$\\frac{\\frac a b}c$}}").toBuild(strictSettings);
+    });
+});
+
 describe("A comment parser", function() {
     it("should parse comments at the end of a line", () => {
         expect("a^2 + b^2 = c^2 % Pythagoras' Theorem\n").toParse();

test/screenshotter/ss_data.yaml

@@ -323,7 +323,11 @@ Phase: 120\text{V}\phase{-78.2^\circ}\;\Large\phase{78.2^\circ}
 Pmb: \mu\pmb{\mu}\pmb{=}\mu\pmb{+}\mu
 PrimeSpacing: f'+f_2'+f^{f'}
 PrimeSuper: x'^2+x'''^2+x'^2_3+x_3'^2
-Raisebox: \frac{a}{a\raisebox{0.5em}{b}} \cdot \frac{a\raisebox{-0.5em}{b}}{a} \cdot \sqrt{a\raisebox{0.5em}{b}} \cdot \sqrt{a\raisebox{-0.5em}{b}} \cdot \sqrt{a\raisebox{0.5em}{b}\raisebox{-0.5em}{b}}
+Raisebox: 
+    \begin{matrix}
+        \frac{a}{a\raisebox{0.5em}{b}} \cdot \frac{a\raisebox{-0.5em}{b}}{a} \cdot \sqrt{a\raisebox{0.5em}{b}} \cdot \sqrt{a\raisebox{-0.5em}{b}} \cdot \sqrt{a\raisebox{0.5em}{b}\raisebox{-0.5em}{b}} \\[2em]
+        a + \left(\vcenter{\hbox{$\frac{a+b}{\dfrac{c}{d}}$}}\right)
+    \end {matrix}
 ReactionArrows: |
     \begin{matrix}
         A \xrightleftarrows{} B \xrightequilibrium{} C \xleftequilibrium{} D \\