feat: Added ability to configure frontmatter parent key

docs/features/breadcrumbs.md

@@ -33,3 +33,59 @@ Want to customize it even more?
 - Component: `quartz/components/Breadcrumbs.tsx`
 - Style: `quartz/components/styles/breadcrumbs.scss`
 - Script: inline at `quartz/components/Breadcrumbs.tsx`
+
+## Using A Frontmatter Prop
+
+ParentBreadcrumbs` is an alternative breadcrumbs component that derives its hierarchy **entirely from frontmatter-defined parent relationships**, rather than folder structure. This is useful for knowledge-base–style sites, wikis, or any content where pages may belong to multiple logical hierarchies.
+
+Unlike the default `Breadcrumbs` component, `ParentBreadcrumbs` supports:
+
+- Explicit parent chains via frontmatter
+- Multiple parents per level
+- Wiki-style links (`[[Page Name]]`)
+- Customizable frontmatter keys
+
+### How It Works
+
+`ParentBreadcrumbs` walks upward through a parent chain starting from the current page, following a configurable frontmatter field.  
+At each level, **all parents are rendered**, while one unvisited parent is chosen to continue the chain upward.
+
+Example frontmatter:
+
+```yaml
+---
+title: "Advanced Topics"
+parent: Basics
+---
+```
+
+Wiki links are supported:
+
+```yaml
+parent: [[Basics]]
+```
+
+Multiple parents:
+
+```yaml
+parent:
+- [[Basics]]
+- [[Reference]]
+```
+
+### Configuration
+
+You can configure `ParentBreadcrumbs` by passing options into `Component.ParentBreadcrumbs()`.
+
+Default configuration:
+
+```ts
+Component.ParentBreadcrumbs({
+  spacerSymbol: "❯",            // symbol displayed between breadcrumb levels
+  rootName: "Home",             // label for the root (index) page
+  resolveFrontmatterTitle: true, // use frontmatter.title instead of slug
+  parentKey: "parent",          // frontmatter key used to resolve parents
+})
+```
+
+All options are optional; omitted values fall back to the defaults.

quartz/components/ParentBreadcrumbs.tsx

@@ -8,16 +8,19 @@ interface ParentBreadcrumbsOptions {
 	spacerSymbol?: string;
 	rootName?: string;
 	resolveFrontmatterTitle?: boolean;
+	frontmatterProp?: string,
 }
 
 const defaultOptions: ParentBreadcrumbsOptions = {
 	spacerSymbol: "❯",
 	rootName: "Home",
 	resolveFrontmatterTitle: true,
+	frontmatterProp: "parent",
 };
 
 export default ((opts?: ParentBreadcrumbsOptions) => {
 	const options = { ...defaultOptions, ...opts };
+	const parentKey = options.frontmatterProp;
 
 	const ParentBreadcrumbs: QuartzComponent = ({
 		fileData,
@@ -34,41 +37,61 @@ export default ((opts?: ParentBreadcrumbsOptions) => {
 
 		const findFile = (name: string) => {
 			const targetSlug = simplifySlug(name as FullSlug);
-
 			return allFiles.find((f: QuartzPluginData) => {
 				const fSlug = simplifySlug(f.slug!);
 				return fSlug === targetSlug || fSlug.endsWith(targetSlug) || f.frontmatter?.title === name;
 			});
 		};
 
-		const crumbs: Array<{ displayName: string; path: string; }> = [];
+		type BreadcrumbNode = { displayName: string; path: string; };
+		const crumbs: Array<BreadcrumbNode[]> = [];
+
 		let current = fileData;
 		const visited = new Set<string>();
 		if (current.slug) visited.add(current.slug);
 
-		while (current && current.frontmatter?.parent) {
-			const parentLink = parseWikiLink(current.frontmatter.parent as string);
-			const parentFile = findFile(parentLink);
+		while (current && current.frontmatter?.[parentKey!]) {
+			const rawParent = current.frontmatter[parentKey!];
+			const parentList = Array.isArray(rawParent) ? rawParent : [rawParent];
 
-			if (parentFile && parentFile.slug && !visited.has(parentFile.slug)) {
-				visited.add(parentFile.slug);
-				crumbs.push({
-					displayName: options.resolveFrontmatterTitle
-						? parentFile.frontmatter?.title ?? parentFile.slug
-						: parentFile.slug,
-					path: resolveRelative(fileData.slug!, parentFile.slug!)
-				});
-				current = parentFile;
+			const currentLevelNodes: BreadcrumbNode[] = [];
+			let nextParent: QuartzPluginData | undefined = undefined;
+
+			for (const p of parentList) {
+				const linkStr = parseWikiLink(p as string);
+				const parentFile = findFile(linkStr);
+
+				if (parentFile && parentFile.slug) {
+					currentLevelNodes.push({
+						displayName: options.resolveFrontmatterTitle
+							? parentFile.frontmatter?.title ?? parentFile.slug
+							: parentFile.slug,
+						path: resolveRelative(fileData.slug!, parentFile.slug!)
+					});
+
+					if (!nextParent && !visited.has(parentFile.slug)) {
+						nextParent = parentFile;
+					}
+				}
+			}
+
+			if (currentLevelNodes.length > 0) {
+				crumbs.push(currentLevelNodes);
+			}
+
+			if (nextParent) {
+				visited.add(nextParent.slug!);
+				current = nextParent;
 			} else {
 				break;
 			}
 		}
 
 		if (current.slug !== "index") {
-			crumbs.push({
+			crumbs.push([{
 				displayName: options.rootName!,
 				path: resolveRelative(fileData.slug!, "index" as SimpleSlug)
-			});
+			}]);
 		}
 
 		crumbs.reverse();
@@ -79,10 +102,15 @@ export default ((opts?: ParentBreadcrumbsOptions) => {
 
 		return (
 			<nav class={classNames(displayClass, "breadcrumb-container")} aria-label="breadcrumbs">
-				{crumbs.map((crumb, index) => (
+				{crumbs.map((crumbLevel, levelIndex) => (
 					<div class="breadcrumb-element">
-						<a href={crumb.path}>{crumb.displayName}</a>
-						{index !== crumbs.length && <p>{options.spacerSymbol}</p>}
+						{crumbLevel.map((node, nodeIndex) => (
+							<>
+								<a href={node.path}>{node.displayName}</a>
+								{nodeIndex < crumbLevel.length - 1 && <span style={{ opacity: 0.5 }}> / </span>}
+							</>
+						))}
+						{levelIndex !== crumbs.length && <p>{options.spacerSymbol}</p>}
 					</div>
 				))}
 				<div class="breadcrumb-element">
@@ -94,4 +122,4 @@ export default ((opts?: ParentBreadcrumbsOptions) => {
 
 	ParentBreadcrumbs.css = style;
 	return ParentBreadcrumbs;
-}) satisfies QuartzComponentConstructor
+}) satisfies QuartzComponentConstructor;