Fix pasting and cmd insertion into the SupSub block of a MathFunction.

src/abstractFields.ts

@@ -162,8 +162,10 @@ export class EditableField extends AbstractMathQuill {
 			if (klass) {
 				const newCmd = new klass(cmd);
 				if (cursor.selection) newCmd.replaces(cursor.replaceSelection());
-				newCmd.createLeftOf(cursor.show());
-				this.__controller.scrollHoriz();
+				if (cursor.parent?.prepareCommandInsertion(cursor, newCmd)) {
+					newCmd.createLeftOf(cursor.show());
+					this.__controller.scrollHoriz();
+				}
 			} else {
 				// TODO: API needs better error reporting
 			}

src/commands/mathBlock.ts

@@ -12,6 +12,7 @@ import { VanillaSymbol, MathElement, MathCommand, Letter, Digit, latexMathParser
 export const writeMethodMixin = <TBase extends Constructor<TNode>>(Base: TBase) =>
 	class extends Base {
 		writeHandler?: (cursor: Cursor, ch: string) => boolean;
+		writeLatexHandler?: (cursor: Cursor, block: MathBlock) => MathBlock | boolean;
 
 		chToCmd(ch: string, options?: Options): TNode {
 			const cons = (CharCmds[ch] as Constructor<TNode> | undefined) || LatexCmds[ch];
@@ -178,16 +179,19 @@ export class MathBlock extends BlockFocusBlur(writeMethodMixin(MathElement)) {
 		const all = Parser.all;
 		const eof = Parser.eof;
 
-		const block = latexMathParser.skip(eof).or(all.result(false)).parse<MathCommand | undefined>(latex);
+		const block = latexMathParser.skip(eof).or(all.result(false)).parse<MathBlock | undefined>(latex);
 
 		if (block && !block.isEmpty() && block.prepareInsertionAt(cursor)) {
-			if (cursor.parent) block.children().adopt(cursor.parent, cursor.left, cursor.right);
-			const elements = block.domify();
+			const handlerResult = this.writeLatexHandler?.(cursor, block);
+			if (handlerResult === true) return;
+			const blockToInsert = handlerResult || block;
+			if (cursor.parent) blockToInsert.children().adopt(cursor.parent, cursor.left, cursor.right);
+			const elements = blockToInsert.domify();
 			cursor.element.before(...elements.contents);
-			cursor.left = block.ends.right;
-			block.finalizeInsert(cursor.options, cursor);
-			block.ends.right?.right?.siblingCreated?.(cursor.options, 'left');
-			block.ends.left?.left?.siblingCreated?.(cursor.options, 'right');
+			cursor.left = blockToInsert.ends.right;
+			blockToInsert.finalizeInsert(cursor.options, cursor);
+			blockToInsert.ends.right?.right?.siblingCreated?.(cursor.options, 'left');
+			blockToInsert.ends.left?.left?.siblingCreated?.(cursor.options, 'right');
 			cursor.parent?.bubble('reflow');
 		}
 	}

src/commands/mathElements.ts

@@ -529,7 +529,7 @@ export class Digit extends VanillaSymbol {
 }
 
 export class Variable extends Symbol {
-	isItalic = false;
+	isItalic = true;
 	isPartOfOperator = false;
 
 	constructor(ch: string, html?: string) {
@@ -1431,8 +1431,6 @@ const BracketMixin = <TBase extends Constructor<MathCommand>>(Base: TBase) =>
 		}
 
 		replaceBracket(brackFrag: HTMLElement, side: Direction) {
-			if (!(this instanceof Bracket) && !(this instanceof MathFunction))
-				throw new Error('can only replace bracket for a Bracket or MathFunction');
 			const symbol = this.getSymbol(side);
 
 			brackFrag.innerHTML = symbol.html;
@@ -1660,6 +1658,36 @@ export class MathFunction extends BracketMixin(MathCommand) {
 			return false;
 		};
 
+		// Only allow a SubSub to be inserted into the block before the parentheses. If anything else is contained in
+		// the block, then move to the content block so it will be inserted there.
+		this.blocks[0].writeLatexHandler = (cursor: Cursor, block: MathBlock) => {
+			if (
+				block.ends.left === block.ends.right &&
+				block.ends.left instanceof Bracket &&
+				block.ends.left.ctrlSeq === '\\left('
+			) {
+				this.enterContentBlock('left', cursor);
+				const bracketContents = block.ends.left.blocks[0].children().disown();
+				block.ends.left.disown();
+				bracketContents.adopt(block);
+				return block;
+			}
+
+			block.eachChild((node: TNode) => {
+				if (node instanceof SupSub) return true;
+				this.enterContentBlock('left', cursor);
+				return false;
+			});
+
+			return false;
+		};
+
+		this.blocks[0].prepareCommandInsertion = (cursor: Cursor, cmd: TNode) => {
+			if (cmd instanceof SupSub) return true;
+			this.enterContentBlock('left', cursor);
+			return true;
+		};
+
 		return super.html();
 	}
 

src/controller.ts

@@ -404,7 +404,6 @@ export class Controller extends ExportText(
 
 	selectAll() {
 		this.notify('move').cursor.insAtRightEnd(this.root);
-		while (this.cursor.left) this.selectLeft();
 		this.withIncrementalSelection((selectDir) => {
 			while (this.cursor.left) selectDir('left');
 		});

src/tree/node.ts

@@ -391,6 +391,9 @@ export class TNode {
 	replaces(_fragment?: string | Fragment) {
 		/* do nothing */
 	}
+	prepareCommandInsertion(_cursor: Cursor, _cmd: TNode): boolean {
+		return true;
+	}
 	setOptions(_options: { text?: () => string; htmlTemplate?: string; latex?: () => string }) {
 		return this;
 	}