From 22dd4f3a28c99bf48a33a126c39f5486bcb01a5e Mon Sep 17 00:00:00 2001
From: Ron Kok <ronkok@comcast.net>
Date: Wed, 22 Nov 2017 05:21:56 -0800
Subject: [PATCH] Append ApplyFunction to math functions (#960)

* Append ApplyFunction to math functions

As described at: https://www.w3.org/TR/REC-MathML/chap3_2.html#sec3.2.4

Character U+2061 is the same as &ApplyFunction;. Ref: https://www.w3schools.com/charsets/ref_html_entities_a.asp

* Add comment for \u2061
---
 src/functions/op.js                    | 8 ++++++--
 src/functions/operatorname.js          | 4 +++-
 test/__snapshots__/mathml-spec.js.snap | 3 +++
 3 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/src/functions/op.js b/src/functions/op.js
index 4f8ff499..285c279d 100644
--- a/src/functions/op.js
+++ b/src/functions/op.js
@@ -209,8 +209,12 @@ const mathmlBuilder = (group, options) => {
         node = new mathMLTree.MathNode(
             "mi", [new mathMLTree.TextNode(group.value.body.slice(1))]);
 
-        // TODO(ron): Append an <mo>&ApplyFunction;</mo> as in \operatorname
-        // ref: https://www.w3.org/TR/REC-MathML/chap3_2.html#sec3.2.2
+        // Append an <mo>&ApplyFunction;</mo>.
+        // ref: https://www.w3.org/TR/REC-MathML/chap3_2.html#sec3.2.4
+        const operator = new mathMLTree.MathNode("mo",
+            [mml.makeText("\u2061", "text")]);
+
+        return new domTree.documentFragment([node, operator]);
     }
 
     return node;
diff --git a/src/functions/operatorname.js b/src/functions/operatorname.js
index ef47d682..1a15b272 100644
--- a/src/functions/operatorname.js
+++ b/src/functions/operatorname.js
@@ -68,8 +68,10 @@ defineFunction({
         const identifier = new mathMLTree.MathNode("mi", output);
         identifier.setAttribute("mathvariant", "normal");
 
+        // \u2061 is the same as &ApplyFunction;
+        // ref: https://www.w3schools.com/charsets/ref_html_entities_a.asp
         const operator = new mathMLTree.MathNode("mo",
-            [mml.makeText("&ApplyFunction;", "text")]);
+            [mml.makeText("\u2061", "text")]);
 
         return new domTree.documentFragment([identifier, operator]);
     },
diff --git a/test/__snapshots__/mathml-spec.js.snap b/test/__snapshots__/mathml-spec.js.snap
index ad4b36d7..3b378772 100644
--- a/test/__snapshots__/mathml-spec.js.snap
+++ b/test/__snapshots__/mathml-spec.js.snap
@@ -27,6 +27,9 @@ exports[`A MathML builder should generate the right types of nodes 1`] = `
       <mi>
         sin
       </mi>
+      <mo>
+        ⁡
+      </mo>
       <mrow>
         <mi>
           x