Fix problems with verification and repair of malformed mtables.

ts/core/MmlTree/MmlNode.ts

@@ -193,8 +193,9 @@ export interface MmlNode extends Node {
    * @param {string} message         The error message to use
    * @param {PropertyList} options   The options telling how much to verify
    * @param {boolean} short          True means use just the kind if not using full errors
+   * @return {MmlNode}               The construted merror
    */
-  mError(message: string, options: PropertyList, short?: boolean): void;
+  mError(message: string, options: PropertyList, short?: boolean): MmlNode;
 
   /**
    * Check integrity of MathML structure
@@ -797,12 +798,14 @@ export abstract class AbstractMmlNode extends AbstractNode implements MmlNode {
    * @param {string} message         The error message to use
    * @param {PropertyList} options   The options telling how much to verify
    * @param {boolean} short          True means use just the kind if not using full errors
+   * @return {MmlNode}               The constructed merror
    */
-  public mError(message: string, options: PropertyList, short: boolean = false) {
+  public mError(message: string, options: PropertyList, short: boolean = false): MmlNode {
     if (this.parent && this.parent.isKind('merror')) {
       return null;
     }
     let merror = this.factory.create('merror');
+    merror.attributes.set('data-mjx-message', message);
     if (options['fullErrors'] || short) {
       let mtext = this.factory.create('mtext');
       let text = this.factory.create('text') as TextNode;
@@ -1189,7 +1192,9 @@ export abstract class AbstractMmlEmptyNode extends AbstractEmptyNode implements
   /**
    *  @override
    */
-  public mError(_message: string, _options: PropertyList, _short: boolean = false) {}
+  public mError(_message: string, _options: PropertyList, _short: boolean = false) {
+    return null as MmlNode;
+  }
 
 }
 

ts/core/MmlTree/MmlNodes/mtable.ts

@@ -137,10 +137,31 @@ export class MmlMtable extends AbstractMmlNode {
    * @override
    */
   protected verifyChildren(options: PropertyList) {
-    if (!options['fixMtables']) {
-      for (const child of this.childNodes) {
-        if (!child.isKind('mtr')) {
-          this.mError('Children of ' + this.kind + ' must be mtr or mlabeledtr', options);
+    let mtr: MmlNode = null;      // all consecutive non-mtr elements are collected into one mtr
+    const factory = this.factory;
+    for (let i = 0; i < this.childNodes.length; i++) {
+      const child = this.childNodes[i];
+      if (child.isKind('mtr')) {
+        mtr = null;               // start a new row if there are non-mtr children
+      } else {
+        const isMtd = child.isKind('mtd');
+        //
+        //  If there is already an mtr for previous children, just remove the child
+        //    otherwise repalce the child with a new mtr
+        //
+        if (mtr) {
+          this.removeChild(child);
+          i--;   // there is one fewer child now
+        } else {
+          mtr = this.replaceChild(factory.create('mtr'), child) as MmlNode;
+        }
+        mtr.appendChild(isMtd ? child : factory.create('mtd', {}, [child]));  // Move the child into the mtr
+        if (!options['fixMtables']) {
+          child.parent.removeChild(child);  // remove the child from its mtd or mtr
+          child.parent = this;              // ... and make it think it is a child of the table again
+          isMtd && mtr.appendChild(factory.create('mtd'));  // child will be replaced, so make sure there is an mtd
+          const merror = child.mError('Children of ' + this.kind + ' must be mtr or mlabeledtr', options, isMtd);
+          mtr.childNodes[mtr.childNodes.length - 1].appendChild(merror);   // append the error to the mtd in the mtr
         }
       }
     }

ts/core/MmlTree/MmlNodes/mtr.ts

@@ -94,11 +94,12 @@ export class MmlMtr extends AbstractMmlNode {
       this.mError(this.kind + ' can only be a child of an mtable', options, true);
       return;
     }
-    if (!options['fixMtables']) {
-      for (const child of this.childNodes) {
-        if (!child.isKind('mtd')) {
-          let mtr = this.replaceChild(this.factory.create('mtr'), child) as MmlNode;
-          mtr.mError('Children of ' + this.kind + ' must be mtd', options, true);
+    for (const child of this.childNodes) {
+      if (!child.isKind('mtd')) {
+        let mtd = this.replaceChild(this.factory.create('mtd'), child) as MmlNode;
+        mtd.appendChild(child);
+        if (!options['fixMtables']) {
+          child.mError('Children of ' + this.kind + ' must be mtd', options);
         }
       }
     }

ts/core/Tree/Node.ts

@@ -96,6 +96,12 @@ export interface Node {
    */
   replaceChild(newChild: Node, oldChild: Node): Node;
 
+  /**
+   * @param {Node} child   Child node to be removed
+   * @return {Node}        The old child node that was removed
+   */
+  removeChild(child: Node): Node;
+
   /**
    * @param {Node} child  A child node whose index in childNodes is desired
    * @return {number}     The index of the child in childNodes, or null if not found
@@ -255,10 +261,23 @@ export abstract class AbstractNode implements Node {
     if (i !== null) {
       this.childNodes[i] = newChild;
       newChild.parent = this;
+      oldChild.parent = null;
     }
     return newChild;
   }
 
+  /**
+   * @override
+   */
+  public removeChild(child: Node) {
+    const i = this.childIndex(child);
+    if (i !== null) {
+      this.childNodes.splice(i, 1);
+      child.parent = null;
+    }
+    return child;
+  }
+
 
   /**
    * @override