Allow unbraced kerns, such as \kern1em.

This is actually the *only* syntax TeX allows; braced kern units
are invalid.

src/Parser.js

@@ -661,6 +661,35 @@ Parser.prototype.parseStringGroup = function(modeName, optional) {
     return firstToken.range(lastToken, str);
 };
 
+/**
+ * Parses a regex-delimited group: the largest sequence of tokens
+ * whose concatenated strings match `regex`. Returns the string
+ * formed by the tokens plus some position information.
+ *
+ * @param {RegExp} regex
+ * @param {string} modeName  Used to describe the mode in error messages
+ */
+Parser.prototype.parseRegexGroup = function(regex, modeName) {
+    var outerMode = this.mode;
+    this.mode = "text";
+    var firstToken = this.nextToken;
+    var lastToken = firstToken;
+    var str = "";
+    while (this.nextToken.text !== "EOF"
+           && regex.test(str + this.nextToken.text)) {
+        lastToken = this.nextToken;
+        str += lastToken.text;
+        this.consume();
+    }
+    if (str === "") {
+        throw new ParseError(
+            "Invalid " + modeName + ": '" + firstToken.text + "'",
+            firstToken);
+    }
+    this.mode = outerMode;
+    return firstToken.range(lastToken, str);
+};
+
 /**
  * Parses a color description.
  */
@@ -682,11 +711,17 @@ Parser.prototype.parseColorGroup = function(optional) {
  * Parses a size specification, consisting of magnitude and unit.
  */
 Parser.prototype.parseSizeGroup = function(optional) {
-    var res = this.parseStringGroup("size", optional);
+    var res;
+    if (!optional && this.nextToken.text !== "{") {
+        res = this.parseRegexGroup(
+            /^[-+]? *(?:$|\d+|\d+\.\d*|\.\d*) *[a-z]{0,2}$/, "size");
+    } else {
+        res = this.parseStringGroup("size", optional);
+    }
     if (!res) {
         return null;
     }
-    var match = (/(-?) *(\d+(?:\.\d*)?|\.\d+) *([a-z]{2})/).exec(res.text);
+    var match = (/([-+]?) *(\d+(?:\.\d*)?|\.\d+) *([a-z]{2})/).exec(res.text);
     if (!match) {
         throw new ParseError("Invalid size: '" + res.text + "'", res);
     }

test/errors-spec.js

@@ -220,7 +220,7 @@ describe("Parser.expect calls:", function() {
         });
         it("complains about missing { for size", function() {
             expect("\\rule{1em}[2em]").toFailWithParseError(
-                   "Expected '{', got '[' at position 11: \\rule{1em}[̲2em]");
+                   "Invalid size: '[' at position 11: \\rule{1em}[̲2em]");
         });
         // Can't test for the [ of an optional group since it's optional
         it("complains about missing } for color", function() {

test/katex-spec.js

@@ -997,6 +997,41 @@ describe("A kern parser", function() {
         var parse = getParsed("\\kern{-1em}")[0];
         expect(parse.value.dimension.number).toBeCloseTo(-1);
     });
+
+    it("should parse positive sizes", function() {
+        var parse = getParsed("\\kern{+1em}")[0];
+        expect(parse.value.dimension.number).toBeCloseTo(1);
+    });
+});
+
+describe("A non-braced kern parser", function() {
+    var emKern = "\\kern1em";
+    var exKern = "\\kern 1 ex";
+    var badUnitRule = "\\kern1px";
+    var noNumberRule = "\\kern em";
+
+    it("should list the correct units", function() {
+        var emParse = getParsed(emKern)[0];
+        var exParse = getParsed(exKern)[0];
+
+        expect(emParse.value.dimension.unit).toEqual("em");
+        expect(exParse.value.dimension.unit).toEqual("ex");
+    });
+
+    it("should not parse invalid units", function() {
+        expect(badUnitRule).toNotParse();
+        expect(noNumberRule).toNotParse();
+    });
+
+    it("should parse negative sizes", function() {
+        var parse = getParsed("\\kern-1em")[0];
+        expect(parse.value.dimension.number).toBeCloseTo(-1);
+    });
+
+    it("should parse positive sizes", function() {
+        var parse = getParsed("\\kern+1em")[0];
+        expect(parse.value.dimension.number).toBeCloseTo(1);
+    });
 });
 
 describe("A left/right parser", function() {