links_add_base_url( string $content, string $base, array $attrs = array('src', 'href') )

Source

File: wp-includes/formatting.php

function links_add_base_url( $content, $base, $attrs = array( 'src', 'href' ) ) {
	global $_links_add_base;
	$_links_add_base = $base;
	$attrs           = implode( '|', (array) $attrs );
	return preg_replace_callback( "!($attrs)=(['\"])(.+?)\\2!i", '_links_add_base', $content );
}