WordPress at a glance
filter is not described

wp_theme_editor_filetypes filter-hook . WP 4.4.0

Filters the list of file types allowed for editing in the Theme editor.

Usage

add_filter( 'wp_theme_editor_filetypes', 'filter_function_name_6530', 10, 2 );
function filter_function_name_6530( $default_types, $theme ){
	// filter...

	return $default_types;
}
$default_types(string[])
List of allowed file types.
$theme(WP_Theme)
The current Theme object.

Where the hook is called

wp_get_theme_file_editable_extensions()
wp_theme_editor_filetypes
wp-admin/includes/file.php 283
$file_types = apply_filters( 'wp_theme_editor_filetypes', $default_types, $theme );

Where the hook is used (in WP core)

Does not used.