https://www.w3schools.com/php/php_filter.asp
Runtime Configurations
The behavior of these functions is affected by settings in php.ini:
  Name: filter.default
  Description: Filter all $_GET, $_POST, $_COOKIE, $_REQUEST and $_SERVER data by this filter. Accepts the name of the filter you like to use by default. See the filter list for the list of the filter names
  Default: "unsafe_raw"
  Changeable: PHP_INI_PERDIR

  Name: filter.default_flags
  Description: Default flags to apply when the default filter is set. This is set to FILTER_FLAG_NO_ENCODE_QUOTES by default for backwards compatibility reasons
  Default: NULL
  Changeable: PHP_INI_PERDIR

PHP 5 Filter Functions:
  filter_has_var() -	Checks if a variable of a specified input type exist
  filter_id() -	Returns the filter ID of a specified filter name
  filter_input() -	Gets an external variable (e.g. from form input) and optionally filters it
  filter_input_array() -	Gets external variables (e.g. from form input) and optionally filters them
  filter_list() -	Returns a list of all supported filters
  filter_var_array() -	Gets multiple variables and filter them
  filter_var() -	Filters a variable with a specified filter

PHP 5 Predefined Filter Constants:
  Constant:	FILTER_VALIDATE_BOOLEAN
  	ID:	258
  	Description: Validates a boolean
  Constant:	FILTER_VALIDATE_EMAIL
  	ID:	274
  	Description: Validates an e-mail address
  Constant:	FILTER_VALIDATE_FLOAT
  	ID:	259
  	Description: Validates a float
  Constant:	FILTER_VALIDATE_INT
  	ID:	257
  	Description: Validates an integer
  Constant:	FILTER_VALIDATE_IP
  	ID:	275
  	Description: Validates an IP address
  Constant:	FILTER_VALIDATE_REGEXP
  	ID:	272
  	Description: Validates a regular expression
  Constant:	FILTER_VALIDATE_URL
  	ID:	273
  	Description: Validates a URL
  Constant:	FILTER_SANITIZE_EMAIL
  	ID:	517
  	Description: Removes all illegal characters from an e-mail address
  Constant:	FILTER_SANITIZE_ENCODED
  	ID:	514
  	Description: Removes/Encodes special characters
  Constant:	FILTER_SANITIZE_MAGIC_QUOTES
  	ID:	521
  	Description: Apply addslashes()
  Constant:	FILTER_SANITIZE_NUMBER_FLOAT
  	ID:	520
  	Description: Remove all characters, except digits, +- and optionally .,eE
  Constant:	FILTER_SANITIZE_NUMBER_INT
  	ID:	519
  	Description: Removes all characters except digits and + -
  Constant:	FILTER_SANITIZE_SPECIAL_CHARS
  	ID:	515
  	Description: Removes special characters
  Constant:	FILTER_SANITIZE_FULL_SPECIAL_CHARS
  Constant:	FILTER_SANITIZE_STRING
  	ID:	513
  	Description: Removes tags/special characters from a string
  Constant:	FILTER_SANITIZE_STRIPPED
  	ID:	513
  	Description: Alias of FILTER_SANITIZE_STRING
  Constant:	FILTER_SANITIZE_URL
  	ID:	518
  	Description: Removes all illegal character from s URL
  Constant:	FILTER_UNSAFE_RAW
  	ID:	516
  	Description: Do nothing, optionally strip/encode special characters
  Constant:	FILTER_CALLBACK
  	ID:	1024
  	Description: Call a user-defined function to filter data

//List the filters:
  <tr><td>int</td><td>257</td></tr><tr><td>boolean</td><td>258</td></tr><tr><td>float</td><td>259</td></tr><tr><td>validate_regexp</td><td>272</td></tr><tr><td>validate_domain</td><td>277</td></tr><tr><td>validate_url</td><td>273</td></tr><tr><td>validate_email</td><td>274</td></tr><tr><td>validate_ip</td><td>275</td></tr><tr><td>validate_mac</td><td>276</td></tr><tr><td>string</td><td>513</td></tr><tr><td>stripped</td><td>513</td></tr><tr><td>encoded</td><td>514</td></tr><tr><td>special_chars</td><td>515</td></tr><tr><td>full_special_chars</td><td>522</td></tr><tr><td>unsafe_raw</td><td>516</td></tr><tr><td>email</td><td>517</td></tr><tr><td>url</td><td>518</td></tr><tr><td>number_int</td><td>519</td></tr><tr><td>number_float</td><td>520</td></tr><tr><td>add_slashes</td><td>523</td></tr><tr><td>callback</td><td>1024</td></tr>
Hello World!
Integer is valid
127.0.0.1 is a valid IP address
john.doe@example.com is a valid email address
https://www.w3schools.com is a valid URL