Support \bmod, \pmod, \pod, and \mod.

src/buildHTML.js

@@ -915,6 +915,59 @@ groupTypes.op = function(group, options) {
     }
 };
 
+groupTypes.mod = function(group, options) {
+    var inner = [];
+
+    if (group.value.modType === "bmod") {
+        // “\nonscript\mskip-\medmuskip\mkern5mu”
+        if (!options.style.isTight()) {
+            inner.push(makeSpan(
+                ["mspace", "negativemediumspace"], [], options));
+        }
+        inner.push(makeSpan(["mspace", "thickspace"], [], options));
+    } else if (options.style.size === Style.DISPLAY.size) {
+        inner.push(makeSpan(["mspace", "quad"], [], options));
+    } else if (group.value.modType === "mod") {
+        inner.push(makeSpan(["mspace", "twelvemuspace"], [], options));
+    } else {
+        inner.push(makeSpan(["mspace", "eightmuspace"], [], options));
+    }
+
+    if (group.value.modType === "pod" || group.value.modType === "pmod") {
+        inner.push(buildCommon.mathsym("(", group.mode));
+    }
+
+    if (group.value.modType !== "pod") {
+        var modInner = [
+            buildCommon.mathsym("m", group.mode),
+            buildCommon.mathsym("o", group.mode),
+            buildCommon.mathsym("d", group.mode)];
+        if (group.value.modType === "bmod") {
+            inner.push(makeSpan(["mbin"], modInner, options));
+            // “\mkern5mu\nonscript\mskip-\medmuskip”
+            inner.push(makeSpan(["mspace", "thickspace"], [], options));
+            if (!options.style.isTight()) {
+                inner.push(makeSpan(
+                    ["mspace", "negativemediumspace"], [], options));
+            }
+        } else {
+            Array.prototype.push.apply(inner, modInner);
+            inner.push(makeSpan(["mspace", "sixmuspace"], [], options));
+        }
+    }
+
+    if (group.value.value) {
+        Array.prototype.push.apply(inner,
+            buildExpression(group.value.value, options, false));
+    }
+
+    if (group.value.modType === "pod" || group.value.modType === "pmod") {
+        inner.push(buildCommon.mathsym(")", group.mode));
+    }
+
+    return buildCommon.makeFragment(inner);
+};
+
 groupTypes.katex = function(group, options) {
     // The KaTeX logo. The offsets for the K and a were chosen to look
     // good, but the offsets for the T, E, and X were taken from the

src/buildMathML.js

@@ -348,6 +348,31 @@ groupTypes.op = function(group, options) {
     return node;
 };
 
+groupTypes.mod = function(group, options) {
+    var inner = [];
+
+    if (group.value.modType === "pod" || group.value.modType === "pmod") {
+        inner.push(new mathMLTree.MathNode(
+            "mo", [makeText("(", group.mode)]));
+    }
+    if (group.value.modType !== "pod") {
+        inner.push(new mathMLTree.MathNode(
+            "mo", [makeText("mod", group.mode)]));
+    }
+    if (group.value.value) {
+        var space = new mathMLTree.MathNode("mspace");
+        space.setAttribute("width", "0.333333em");
+        inner.push(space);
+        inner = inner.concat(buildExpression(group.value.value, options));
+    }
+    if (group.value.modType === "pod" || group.value.modType === "pmod") {
+        inner.push(new mathMLTree.MathNode(
+            "mo", [makeText(")", group.mode)]));
+    }
+
+    return new mathMLTree.MathNode("mo", inner);
+};
+
 groupTypes.katex = function(group) {
     var node = new mathMLTree.MathNode(
         "mtext", [new mathMLTree.TextNode("KaTeX")]);

src/functions.js

@@ -279,6 +279,28 @@ defineFunction("\\stackrel", {
     };
 });
 
+// \mod-type functions
+defineFunction("\\bmod", {
+    numArgs: 0,
+}, function(context, args) {
+    return {
+        type: "mod",
+        modType: "bmod",
+        value: null,
+    };
+});
+
+defineFunction(["\\pod", "\\pmod", "\\mod"], {
+    numArgs: 1,
+}, function(context, args) {
+    var body = args[0];
+    return {
+        type: "mod",
+        modType: context.funcName.substr(1),
+        value: ordargument(body),
+    };
+});
+
 // Extra data needed for the delimiter handler down below
 var delimiterSizes = {
     "\\bigl" : {mclass: "mopen",    size: 1},

static/katex.less

@@ -105,9 +105,9 @@
     @ptperem: 10.0;
     @nulldelimiterspace: 1.2em / @ptperem;
 
-    @thinspace: 0.16667em;
+    @thinspace: 0.16667em;      // 3mu
-    @mediumspace: 0.22222em;
+    @mediumspace: 0.22222em;    // 4mu
-    @thickspace: 0.27778em;
+    @thickspace: 0.27778em;     // 5mu
 
     // These spacings apply in textstyle and displaystyle.
     .mord {
@@ -300,6 +300,10 @@
             width: @thinspace;
         }
 
+        &.negativemediumspace {
+            margin-left: -@mediumspace;
+        }
+
         &.mediumspace {
             width: @mediumspace;
         }
@@ -308,10 +312,22 @@
             width: @thickspace;
         }
 
+        &.sixmuspace {
+            width: 0.333333em;
+        }
+
+        &.eightmuspace {
+            width: 0.444444em;
+        }
+
         &.enspace {
             width: 0.5em;
         }
 
+        &.twelvemuspace {
+            width: 0.666667em;
+        }
+
         &.quad {
             width: 1em;
         }

test/screenshotter/ss_data.yaml

@@ -92,6 +92,18 @@ MathRm: \mathrm{Ax2k\breve{a}\omega\Omega\imath+\KaTeX}
 MathSf: \mathsf{Ax2k\breve{a}\omega\Omega\imath+\KaTeX}
 MathScr: \mathscr{Ax2k\breve{a}\omega\Omega\imath+\KaTeX}
 MathTt: \mathtt{Ax2k\breve{a}\omega\Omega\imath+\KaTeX}
+Mod: |
+    \begin{array}{cc}
+        a \bmod 2 & b \pod 3 \\
+        c \pmod{4} & d \mod{56} \\
+        \displaystyle a\bmod 2 & \displaystyle b \pod 3 \\
+        \displaystyle c\pmod{4} & \displaystyle d \mod{56}
+    \end{array}
+ModScript: |
+    \begin{array}{cc}
+        \scriptstyle a\bmod 2 & \scriptstyle b \pod 3 \\
+        \scriptstyle c\pmod{4} & \scriptstyle d \mod{56}
+    \end{array}
 NegativeSpaceBetweenRel: A =\!= B
 NestedFractions: |
     \dfrac{\frac{a}{b}}{\frac{c}{d}}\dfrac{\dfrac{a}{b}}