Fix \not vertical alignment (#1497)

* Fix \not vertical alignment

Fix #1491 by changing from `position: absolute` to `position: relative`.

* Switch to \rlap implementation of \not

* Separate \not the macro from \not the symbol via \@not

* Fix test

src/buildHTML.js

@@ -183,15 +183,6 @@ export const buildExpression = function(
         }
     }
 
-    // Process \\not commands within the group.
-    for (let i = 0; i < groups.length; i++) {
-        const group = groups[i];
-        if (group instanceof domTree.symbolNode && group.value === "\u0338") {
-            // Results in a solidus being overlaid over the following group/atom.
-            group.style.position = "absolute";
-        }
-    }
-
     return groups;
 };
 

src/macros.js

@@ -357,6 +357,12 @@ defineMacro("\\llap", "\\mathllap{\\textrm{#1}}");
 defineMacro("\\rlap", "\\mathrlap{\\textrm{#1}}");
 defineMacro("\\clap", "\\mathclap{\\textrm{#1}}");
 
+// \not is defined by base/fontmath.ltx via
+// \DeclareMathSymbol{\not}{\mathrel}{symbols}{"36}
+// It's thus treated like a \mathrel, but defined by a symbol that has zero
+// width but extends to the right.  We use \rlap to get that spacing.
+defineMacro("\\not", '\\mathrel{\\mathrlap\\@not}');
+
 // Negated symbols from base/fontmath.ltx:
 // \def\neq{\not=} \let\ne=\neq
 // \DeclareRobustCommand

src/symbols.js

@@ -563,7 +563,7 @@ defineSymbol(math, main, rel, "\u2265", "\\geq", true);
 defineSymbol(math, main, rel, "\u2190", "\\gets");
 defineSymbol(math, main, rel, ">", "\\gt");
 defineSymbol(math, main, rel, "\u2208", "\\in", true);
-defineSymbol(math, main, rel, "\u0338", "\\not");
+defineSymbol(math, main, rel, "\u0338", "\\@not");
 defineSymbol(math, main, rel, "\u2282", "\\subset", true);
 defineSymbol(math, main, rel, "\u2283", "\\supset", true);
 defineSymbol(math, main, rel, "\u2286", "\\subseteq", true);

test/katex-spec.js

@@ -93,8 +93,12 @@ describe("A rel parser", function() {
             if (group.type === "htmlmathml") {
                 group = group.value.html[0];
             }
+            if (group.type === "mclass") {
+                expect(group.value.mclass).toEqual("mrel");
+            } else {
                 expect(group.type).toEqual("rel");
             }
+        }
     });
 });