Use this function to get a list of all the supported filters (those we just had a look at). It will give you an array of human readable names associated with each filter (see the manual pages for those names).

The indexes have no meaning; it is simply a numeric array. As with all of these filter related functions, this is available only as of PHP 5.2.0.

$list = filter_list();
/*
array (
  0 => 'int',
  1 => 'boolean',
  2 => 'float',
  3 => 'validate_regexp',
  4 => 'validate_url',
  5 => 'validate_email',
  6 => 'validate_ip',
  7 => 'string',
  8 => 'stripped',
  9 => 'encoded',
  10 => 'special_chars',
  11 => 'unsafe_raw',
  12 => 'email',
  13 => 'url',
  14 => 'number_int',
  15 => 'number_float',
  16 => 'magic_quotes',
  17 => 'callback'
)
*/
See the manual entry for filter_list()