wp-includes/theme.php:415Registers a directory that contains themes.
$directorystringboolfunction register_theme_directory( $directory ) { global $wp_theme_directories; if ( ! file_exists( $directory ) ) { // Try prepending as the theme directory could be relative to the content directory. $directory = WP_CONTENT_DIR . '/' . $directory; // If this directory does not exist, return and do not register. if ( ! file_exists( $directory ) ) { return false; } } if ( ! is_array( $wp_theme_directories ) ) { $wp_theme_directories = array(); } $untrailed = untrailingslashit( $directory ); if ( ! empty( $untrailed ) && ! in_array( $untrailed, $wp_theme_directories, true ) ) { $wp_theme_directories[] = $untrailed; } return true;}Introduced in 2.9.0. Unchanged from 6.7.7 through 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
src/wp-includes/theme.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.