wp_img_tag_add_loading_attr

wp_img_tag_add_loading_attr是一个给HTML img标签添加加载属性的函数。加载属性指定了图片的加载方式，它可以取三个值。”eager”表示立即加载，”lazy”表示只在图像进入视图时加载，”auto”表示让浏览器决定。

为`img`HTML标签添加`loading`属性。

function wp_img_tag_add_loading_attr( $image, $context ) {
	// Get loading attribute value to use. This must occur before the conditional check below so that even images that
	// are ineligible for being lazy-loaded are considered.
	$value = wp_get_loading_attr_default( $context );

	// Images should have source and dimension attributes for the `loading` attribute to be added.
	if ( false === strpos( $image, ' src="' ) || false === strpos( $image, ' width="' ) || false === strpos( $image, ' height="' ) ) {
		return $image;
	}

	/**
	 * Filters the `loading` attribute value to add to an image. Default `lazy`.
	 *
	 * Returning `false` or an empty string will not add the attribute.
	 * Returning `true` will add the default value.
	 *
	 * @since 5.5.0
	 *
	 * @param string|bool $value   The `loading` attribute value. Returning a falsey value will result in
	 *                             the attribute being omitted for the image.
	 * @param string      $image   The HTML `img` tag to be filtered.
	 * @param string      $context Additional context about how the function was called or where the img tag is.
	 */
	$value = apply_filters( 'wp_img_tag_add_loading_attr', $value, $image, $context );

	if ( $value ) {
		if ( ! in_array( $value, array( 'lazy', 'eager' ), true ) ) {
			$value = 'lazy';
		}

		return str_replace( '<img', '<img loading="' . esc_attr( $value ) . '"', $image );
	}

	return $image;
}