This function had been marked as deprecated.

Callback function for ob_start() to capture all links in the theme.

Signature

preview_theme_ob_filter( $content )
content
 (string)

Return

(string)

Source

function preview_theme_ob_filter( $content ) {
	_deprecated_function( __FUNCTION__, '4.3.0' );
	return $content;
}
WP Trac GitHub

Link here