subtree, with 
 elements rendered as
	 * newlines (textContent drops them, flattening multi-line content).
	 *
	 * @param \DOMNode $node Node.
	 * @return string
	 */
	private static function pre_text( $node ) {
		$out = '';
		foreach ( $node->childNodes as $child ) {
			if ( XML_TEXT_NODE === $child->nodeType ) {
				$out .= $child->nodeValue;
			} elseif ( XML_ELEMENT_NODE === $child->nodeType ) {
				$out .= 'br' === strtolower( $child->nodeName ) ? "\n" : self::pre_text( $child );
			}
		}
		return $out;
	}

	/**
	 * Render a  as a GitHub-flavored markdown pipe table. The first row
	 * (thead's, or simply the first ) becomes the header row.
	 *
	 * @param \DOMNode $node Table node.
	 * @return string '' when the table has no rows.
	 */
	private static function table_node( $node ) {
		$rows = array();
		foreach ( $node->childNodes as $child ) {
			if ( XML_ELEMENT_NODE !== $child->nodeType ) {
				continue;
			}
			$t = strtolower( $child->nodeName );
			if ( 'tr' === $t ) {
				$rows[] = $child;
			} elseif ( in_array( $t, array( 'thead', 'tbody', 'tfoot' ), true ) ) {
				foreach ( $child->childNodes as $tr ) {
					if ( XML_ELEMENT_NODE === $tr->nodeType && 'tr' === strtolower( $tr->nodeName ) ) {
						$rows[] = $tr;
					}
				}
			}
		}

		$grid = array();
		foreach ( $rows as $tr ) {
			$cells = array();
			foreach ( $tr->childNodes as $cell ) {
				if ( XML_ELEMENT_NODE !== $cell->nodeType ) {
					continue;
				}
				$ct = strtolower( $cell->nodeName );
				if ( 'td' !== $ct && 'th' !== $ct ) {
					continue;
				}
				// Cell content is inline in a pipe table: collapse block spacing to a
				// space and escape literal pipes so they can't break the row.
				$text    = trim( preg_replace( '/\s+/', ' ', self::children( $cell ) ) );
				$cells[] = str_replace( '|', '\\|', $text );
			}
			if ( ! empty( $cells ) ) {
				$grid[] = $cells;
			}
		}
		if ( empty( $grid ) ) {
			return '';
		}

		$cols = 0;
		foreach ( $grid as $r ) {
			$cols = max( $cols, count( $r ) );
		}
		$lines = array();
		foreach ( $grid as $i => $r ) {
			$lines[] = '| ' . implode( ' | ', array_pad( $r, $cols, '' ) ) . ' |';
			if ( 0 === $i ) {
				$lines[] = '|' . str_repeat( ' --- |', $cols );
			}
		}
		return implode( "\n", $lines );
	}

	/**
	 * One playlist track as a readable line: **Title** — Artist (3:21).
	 *
	 * @param \DOMNode $button Track button node.
	 * @return string '' when the expected title span is missing (caller falls back).
	 */
	private static function playlist_track( $button ) {
		$title = self::normal_text( self::find_by_class( $button, 'wp-block-playlist-track__title' ) );
		if ( '' === $title ) {
			return '';
		}
		$artist = self::normal_text( self::find_by_class( $button, 'wp-block-playlist-track__artist' ) );
		// Own text nodes only: the length span nests a screen-reader "Duration: "
		// prefix that would read doubly ("(Duration: 3:21)").
		$length = self::own_text( self::find_by_class( $button, 'wp-block-playlist-track__length' ) );

		$line = '**' . $title . '**';
		if ( '' !== $artist ) {
			$line .= ' — ' . $artist;
		}
		if ( '' !== $length ) {
			$line .= ' (' . $length . ')';
		}
		return $line;
	}

	/**
	 * The text of the element an aria-labelledby points at (first ID), '' if unresolvable.
	 *
	 * @param \DOMNode $node Labelled node.
	 * @return string
	 */
	private static function labelled_by( $node ) {
		$ids = preg_split( '/\s+/', trim( (string) $node->getAttribute( 'aria-labelledby' ) ), -1, PREG_SPLIT_NO_EMPTY );
		if ( empty( $ids ) || ! $node->ownerDocument ) {
			return '';
		}
		$ref = $node->ownerDocument->getElementById( $ids[0] );
		return $ref ? self::normal_text( $ref ) : '';
	}

	/**
	 * Whether an element carries a class (exact token match).
	 *
	 * @param \DOMNode $node  Element.
	 * @param string   $class Class name.
	 * @return bool
	 */
	private static function has_class( $node, $class ) {
		$classes = preg_split( '/\s+/', (string) $node->getAttribute( 'class' ), -1, PREG_SPLIT_NO_EMPTY );
		return in_array( $class, $classes, true );
	}

	/**
	 * First descendant element with a class, or null.
	 *
	 * @param \DOMNode $node  Subtree root.
	 * @param string   $class Class name.
	 * @return \DOMNode|null
	 */
	private static function find_by_class( $node, $class ) {
		foreach ( $node->childNodes as $child ) {
			if ( XML_ELEMENT_NODE !== $child->nodeType ) {
				continue;
			}
			if ( self::has_class( $child, $class ) ) {
				return $child;
			}
			$hit = self::find_by_class( $child, $class );
			if ( $hit ) {
				return $hit;
			}
		}
		return null;
	}

	/**
	 * Whitespace-normalized textContent of an element ('' for null).
	 *
	 * @param \DOMNode|null $node Element or null.
	 * @return string
	 */
	private static function normal_text( $node ) {
		return $node ? trim( preg_replace( '/\s+/', ' ', $node->textContent ) ) : '';
	}

	/**
	 * Whitespace-normalized text of an element's DIRECT text-node children only
	 * ('' for null) — skips nested elements like screen-reader spans.
	 *
	 * @param \DOMNode|null $node Element or null.
	 * @return string
	 */
	private static function own_text( $node ) {
		if ( ! $node ) {
			return '';
		}
		$out = '';
		foreach ( $node->childNodes as $child ) {
			if ( XML_TEXT_NODE === $child->nodeType ) {
				$out .= $child->nodeValue;
			}
		}
		return trim( preg_replace( '/\s+/', ' ', $out ) );
	}

	/**
	 * Plain text from HTML.
	 *
	 * @param string $html HTML.
	 * @return string
	 */
	private static function text( $html ) {
		return trim( html_entity_decode( wp_strip_all_tags( (string) $html ), ENT_QUOTES | ENT_HTML5, 'UTF-8' ) );
	}
}