quoteModifiers can be autoloaded from your $plugins_dir (also see: Naming Conventions) or can be registered explicitely (see: register_modifier). Additionally all php-functions can be used as modifiers implicitely. (The @count-example above actually uses php's count-function and not a smarty-modifier). Using php-functions as modifiers has two little pitfalls: First: Sometimes the order of the function-parameters is not the desirable one ({"%2.f"|sprintf:$float} actually works, but asks for the more intuitive {For example: $float|string_format:"%2.f"} that is provided by the Smarty distribution). Second: with $security turned on all php-functions that are to be used as modifiers have to be declared trusted in the $security_settings['MODIFIER_FUNCS']-array.
quoteModifiers can be autoloaded from your