Update render.php

block/build/render.php

@@ -2,13 +2,31 @@
 
 namespace HM\TOC;
 
+use WP_HTML_Tag_Processor;
+
 $post_id = isset( $attributes['postId'] ) ? $attributes['postId'] : ( $block->context['postId'] ?? null );
 $post = get_post( $post_id );
 
 if ( ! $post ) {
 	return;
 }
 
+$max_level = $attributes['maxLevel'] ?? 3;
+
+// Work out the current level by finding the heighest level heading within the content.
+// Typically this is H2. But technically it can be anything.
+foreach ( array_slice( [ 'h1', 'h2', 'h3', 'h4', 'h5', 'h6' ], 0, $max_level ) as $i => $heading_tag ) {
+	$tags = new WP_HTML_Tag_Processor( $post->post_content );
+	if ( $tags->next_tag( $heading_tag ) ) {
+		$current_level = $i + 1;
+		break;
+	}
+}
+
+if ( ! $current_level ) {
+	return;
+}
+
 $hierarchy = get_header_hierarchy( $post );
 
 if ( empty( $hierarchy ) ) {
@@ -23,6 +41,5 @@
 );
 
 printf( '<h2>%s</h2>', esc_html__( 'Table of contents', 'hm-table-of-contents' ) );
-the_heading_list( $hierarchy, $attributes['maxLevel'] ?? 3 );
-
+the_heading_list( $hierarchy, $max_level, $current_level );
 echo '</div>';