Support "mu" units for sizes.

18mu is 1em.

And use emPerEx when converting ex to em, rather than xHeight.
(Previously some places used emPerEx and others used xHeight.)

src/Parser.js

@@ -733,7 +733,7 @@ Parser.prototype.parseSizeGroup = function(optional) {
         number: +(match[1] + match[2]), // sign + magnitude, cast to number
         unit: match[3],
     };
-    if (data.unit !== "em" && data.unit !== "ex") {
+    if (data.unit !== "em" && data.unit !== "ex" && data.unit !== "mu") {
         throw new ParseError("Invalid unit: '" + data.unit + "'", res);
     }
     return new ParseFuncOrArgument(

src/buildHTML.js

@@ -543,6 +543,16 @@ groupTypes.genfrac = function(group, options) {
         options);
 };
 
+var calculateSize = function(sizeValue, style) {
+    var x = sizeValue.number;
+    if (sizeValue.unit === "ex") {
+        x *= style.metrics.emPerEx;
+    } else if (sizeValue.unit === "mu") {
+        x /= 18;
+    }
+    return x;
+};
+
 groupTypes.array = function(group, options) {
     var r;
     var c;
@@ -589,18 +599,7 @@ groupTypes.array = function(group, options) {
 
         var gap = 0;
         if (group.value.rowGaps[r]) {
-            gap = group.value.rowGaps[r].value;
+            gap = calculateSize(group.value.rowGaps[r].value, style);
-            switch (gap.unit) {
-                case "em":
-                    gap = gap.number;
-                    break;
-                case "ex":
-                    gap = gap.number * style.metrics.emPerEx;
-                    break;
-                default:
-                    console.error("Can't handle unit " + gap.unit);
-                    gap = 0;
-            }
             if (gap > 0) { // \@argarraycr
                 gap += arstrutDepth;
                 if (depth < gap) {
@@ -1269,21 +1268,11 @@ groupTypes.rule = function(group, options) {
     // Calculate the shift, width, and height of the rule, and account for units
     var shift = 0;
     if (group.value.shift) {
-        shift = group.value.shift.number;
+        shift = calculateSize(group.value.shift, style);
-        if (group.value.shift.unit === "ex") {
-            shift *= style.metrics.xHeight;
-        }
     }
 
-    var width = group.value.width.number;
+    var width = calculateSize(group.value.width, style);
-    if (group.value.width.unit === "ex") {
+    var height = calculateSize(group.value.height, style);
-        width *= style.metrics.xHeight;
-    }
-
-    var height = group.value.height.number;
-    if (group.value.height.unit === "ex") {
-        height *= style.metrics.xHeight;
-    }
 
     // The sizes of rules are absolute, so make it larger if we are in a
     // smaller style.
@@ -1311,10 +1300,7 @@ groupTypes.kern = function(group, options) {
 
     var dimension = 0;
     if (group.value.dimension) {
-        dimension = group.value.dimension.number;
+        dimension = calculateSize(group.value.dimension, style);
-        if (group.value.dimension.unit === "ex") {
-            dimension *= style.metrics.xHeight;
-        }
     }
 
     dimension /= style.sizeMultiplier;

test/katex-spec.js

@@ -977,15 +977,18 @@ describe("A rule parser", function() {
 describe("A kern parser", function() {
     var emKern = "\\kern{1em}";
     var exKern = "\\kern{1ex}";
+    var muKern = "\\kern{1mu}";
     var badUnitRule = "\\kern{1px}";
     var noNumberRule = "\\kern{em}";
 
     it("should list the correct units", function() {
         var emParse = getParsed(emKern)[0];
         var exParse = getParsed(exKern)[0];
+        var muParse = getParsed(muKern)[0];
 
         expect(emParse.value.dimension.unit).toEqual("em");
         expect(exParse.value.dimension.unit).toEqual("ex");
+        expect(muParse.value.dimension.unit).toEqual("mu");
     });
 
     it("should not parse invalid units", function() {
@@ -1007,15 +1010,18 @@ describe("A kern parser", function() {
 describe("A non-braced kern parser", function() {
     var emKern = "\\kern1em";
     var exKern = "\\kern 1 ex";
+    var muKern = "\\kern 1mu";
     var badUnitRule = "\\kern1px";
     var noNumberRule = "\\kern em";
 
     it("should list the correct units", function() {
         var emParse = getParsed(emKern)[0];
         var exParse = getParsed(exKern)[0];
+        var muParse = getParsed(muKern)[0];
 
         expect(emParse.value.dimension.unit).toEqual("em");
         expect(exParse.value.dimension.unit).toEqual("ex");
+        expect(muParse.value.dimension.unit).toEqual("mu");
     });
 
     it("should not parse invalid units", function() {