feat: Support \underbar (#2713)

* feat: Support \underbar

* Update screenshots

docs/support_table.md

@@ -1123,6 +1123,7 @@ use `\ce` instead|
 |\uArr|$\uArr$||
 |\uarr|$\uarr$||
 |\ulcorner|$\ulcorner$||
+|\underbar|$\underbar{X}$|`\underbar{X}`|
 |\underbrace|$\underbrace{x+⋯+x}_{n\text{ times}}$|`\underbrace{x+⋯+x}_{n\text{ times}}`|
 |\underbracket|<span style="color:firebrick;">Not supported</span>||
 |\undergroup|$\undergroup{AB}$|`\undergroup{AB}`|

docs/supported.md

@@ -33,7 +33,7 @@ table td {
 |$\ddot{a}$ `\ddot{a}`  |$\underleftrightarrow{AB}$ `\underleftrightarrow{AB}`|$\underbrace{AB}$ `\underbrace{AB}`
 |$\grave{a}$ `\grave{a}`|$\overline{AB}$ `\overline{AB}` |$\overlinesegment{AB}$ `\overlinesegment{AB}`
 |$\hat{\theta}$ `\hat{\theta}`|$\underline{AB}$ `\underline{AB}`  |$\underlinesegment{AB}$ `\underlinesegment{AB}`
-|$\widehat{ac}$ `\widehat{ac}`|$\widecheck{ac}$ `\widecheck{ac}`  |
+|$\widehat{ac}$ `\widehat{ac}`|$\widecheck{ac}$ `\widecheck{ac}`  |$\underbar{X}$ `\underbar{X}`
 
 ***Accent functions inside \\text{…}***
 

src/macros.js

@@ -377,6 +377,9 @@ defineMacro("\\clap", "\\mathclap{\\textrm{#1}}");
 // \mathstrut from the TeXbook, p 360
 defineMacro("\\mathstrut", "\\vphantom{(}");
 
+// \underbar from TeXbook p 353
+defineMacro("\\underbar", "\\underline{\\text{#1}}");
+
 // \not is defined by base/fontmath.ltx via
 // \DeclareMathSymbol{\not}{\mathrel}{symbols}{"36}
 // It's thus treated like a \mathrel, but defined by a symbol that has zero

test/katex-spec.js

@@ -2163,6 +2163,7 @@ describe("An accent parser", function() {
         expect`\vec{x^2}`.toParse();
         expect`\vec{x}^2`.toParse();
         expect`\vec x`.toParse();
+        expect("\\underbar{X}").toParse();
     });
 
     it("should produce accents", function() {

test/screenshotter/ss_data.yaml

@@ -13,7 +13,7 @@
 # writing | (or >) as the first symbol of the value and then continuing
 # on the next line. See http://www.yaml.org/ for syntax details.
 
-Accents: \vec{A}\vec{x}\vec x^2\vec{x}_2^2\vec{A}^2\vec{xA}^2
+Accents: \vec{A}\vec{x}\vec x^2\vec{x}_2^2\vec{A}^2\vec{xA}^2\; \underbar{X}
 AccentsText: |
     \begin{array}{lccccc}
     \text{\'\i} & \text{\.\i} & \text{\`\i} & \text{\"\i} & \text{\H\i} & \text{\r\i} \\