Support \pmb (#1418)

* Support \pmb

* Fix lint error

* Add phony screenshots

* Screenshots take two

* Screenshots take three

* Simplify copies

* Move determination of mclass from handler to htmlBuilder

* Change to a macro definition

* Update screenshots

* Pick up review comments

* Clean up nesting of braces

* Update screenshot

src/macros.js

@@ -659,6 +659,15 @@ defineMacro("\\mod", "\\allowbreak" +
     "\\mathchoice{\\mkern18mu}{\\mkern12mu}{\\mkern12mu}{\\mkern12mu}" +
     "{\\rm mod}\\,\\,#1");
 
+// \pmb    --   A simulation of bold.
+// It works by typesetting three copies of the argument with small offsets.
+// Ref: a rather lengthy macro in ambsy.sty
+defineMacro("\\pmb", "\\html@mathml{\\@binrel{#1}{" +
+    "\\mathrlap{#1}" +
+    "\\mathrlap{\\mkern0.4mu\\raisebox{0.4mu}{$#1$}}" +
+    "{\\mkern0.8mu#1}" +
+    "}}{\\mathbf{#1}}");
+
 //////////////////////////////////////////////////////////////////////
 // LaTeX source2e
 

test/katex-spec.js

@@ -1535,6 +1535,17 @@ describe("A font parser", function() {
     });
 });
 
+describe("A \\pmb builder", function() {
+    it("should not fail", function() {
+        expect("\\pmb{\\mu}").toBuild();
+        expect("\\pmb{=}").toBuild();
+        expect("\\pmb{+}").toBuild();
+        expect("\\pmb{\\frac{x^2}{x_1}}").toBuild();
+        expect("\\pmb{}").toBuild();
+        expect("\\def\\x{1}\\pmb{\\x\\def\\x{2}}").toParseLike("\\pmb{1}");
+    });
+});
+
 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

@@ -274,6 +274,7 @@ Phantom: \begin{array}{l}
             \dfrac{1+\phantom{x^{\blue{2}}} = x}{1+x^{\blue{2}} = x} \left(\vphantom{\int_t} zzz \right) \left( X \hphantom{\frac{\frac X X}{X}} \right)\\
             \text{a \phantom{123} b \hphantom{45678} c \vphantom{101112} d}
          \end{array}
+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}}