Properly handle additional attributes during inheritance (make copy of attributes so they don't get changed permanently).

Author: dpvc

mathjax3-ts/core/MmlTree/MmlNodes/mtable.ts

@@ -84,8 +84,10 @@ export class MmlMtable extends AbstractMmlNode {
             }
         }
         display = !!(this.attributes.getExplicit('displaystyle') || this.attributes.getDefault('displaystyle'));
-        attributes.columnalign = [this.kind, this.attributes.get('columnalign')];
-        attributes.rowalign = [this.kind, 'center'];
+        attributes = this.addInheritedAttributes(attributes, {
+            columnalign: this.attributes.get('columnalign'),
+            rowalign: 'center'
+        });
         const ralign = (this.attributes.get('rowalign') as string)
                      .replace(/^\s+/, '').replace(/\s+$/, '').split(/ +/);
         for (const child of this.childNodes) {

mathjax3-ts/core/MmlTree/MmlNodes/mtr.ts

@@ -64,10 +64,15 @@ export class MmlMtr extends AbstractMmlNode {
                     .appendChild(child);
             }
         }
-        attributes.rowalign = [this.kind, this.attributes.get('rowalign')];
-        attributes.columnalign = [this.kind, 'center'];
         const calign = (this.attributes.get('columnalign') as string)
                        .replace(/^\s+/, '').replace(/\s+$/, '').split(/ +/);
+        if (this.arity === 1) {
+            calign.unshift(this.parent.attributes.get('side') as string);
+        }
+        attributes = this.addInheritedAttributes(attributes, {
+            rowalign: this.attributes.get('rowalign'),
+            columnalign: 'center'
+        });
         for (const child of this.childNodes) {
             attributes.columnalign[1] = calign.shift() || attributes.columnalign[1];
             child.setInheritedAttributes(attributes, display, level, prime);