| ID | Used with | Description | 
|---|---|---|
FILTER_FLAG_STRIP_LOW | 
       
        FILTER_SANITIZE_ENCODED,
        FILTER_SANITIZE_SPECIAL_CHARS,
        FILTER_SANITIZE_STRING,
        FILTER_UNSAFE_RAW
        | 
       Strips characters that have a numerical value <32. | 
FILTER_FLAG_STRIP_HIGH | 
       
        FILTER_SANITIZE_ENCODED,
        FILTER_SANITIZE_SPECIAL_CHARS,
        FILTER_SANITIZE_STRING,
        FILTER_UNSAFE_RAW
        | 
       Strips characters that have a numerical value >127. | 
FILTER_FLAG_STRIP_BACKTICK | 
       
        FILTER_SANITIZE_ENCODED,
        FILTER_SANITIZE_SPECIAL_CHARS,
        FILTER_SANITIZE_STRING,
        FILTER_UNSAFE_RAW
        | 
       Strips backtick characters. | 
FILTER_FLAG_ALLOW_FRACTION | 
       
        FILTER_SANITIZE_NUMBER_FLOAT
        | 
       Allows a period (.) as a fractional separator in numbers. | 
FILTER_FLAG_ALLOW_THOUSAND | 
       
        FILTER_SANITIZE_NUMBER_FLOAT,
        FILTER_VALIDATE_FLOAT
        | 
       Allows a comma (,) as a thousands separator in numbers. | 
FILTER_FLAG_ALLOW_SCIENTIFIC | 
       
        FILTER_SANITIZE_NUMBER_FLOAT
        | 
       Allows an e or E for scientific notation in numbers. | 
FILTER_FLAG_NO_ENCODE_QUOTES | 
       
        FILTER_SANITIZE_STRING
        | 
       If this flag is present, single (') and double (") quotes will not be encoded. | 
FILTER_FLAG_ENCODE_LOW | 
       
        FILTER_SANITIZE_ENCODED,
        FILTER_SANITIZE_STRING,
        FILTER_SANITIZE_RAW
        | 
       Encodes all characters with a numerical value <32. | 
FILTER_FLAG_ENCODE_HIGH | 
       
        FILTER_SANITIZE_ENCODED,
        FILTER_SANITIZE_SPECIAL_CHARS,
        FILTER_SANITIZE_STRING,
        FILTER_SANITIZE_RAW
        | 
       Encodes all characters with a numerical value >127. | 
FILTER_FLAG_ENCODE_AMP | 
       
        FILTER_SANITIZE_STRING,
        FILTER_SANITIZE_RAW
        | 
       Encodes ampersands (&). | 
FILTER_NULL_ON_FAILURE | 
       
        FILTER_VALIDATE_BOOLEAN
        | 
       
        Returns NULL for unrecognized boolean values.
        | 
      
FILTER_FLAG_ALLOW_OCTAL | 
       
        FILTER_VALIDATE_INT
        | 
       Regards inputs starting with a zero (0) as octal numbers. This only allows the succeeding digits to be 0-7. | 
FILTER_FLAG_ALLOW_HEX | 
       
        FILTER_VALIDATE_INT
        | 
       Regards inputs starting with 0x or 0X as hexadecimal numbers. This only allows succeeding characters to be a-fA-F0-9. | 
FILTER_FLAG_EMAIL_UNICODE | 
       
        FILTER_VALIDATE_EMAIL
        | 
       Allows the local part of the email address to contain Unicode characters. | 
FILTER_FLAG_IPV4 | 
       
        FILTER_VALIDATE_IP
        | 
       Allows the IP address to be in IPv4 format. | 
FILTER_FLAG_IPV6 | 
       
        FILTER_VALIDATE_IP
        | 
       Allows the IP address to be in IPv6 format. | 
FILTER_FLAG_NO_PRIV_RANGE | 
       
        FILTER_VALIDATE_IP
        | 
       
         Fails validation for the following private IPv4 ranges: 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16. Fails validation for the IPv6 addresses starting with FD or FC.  | 
      
FILTER_FLAG_NO_RES_RANGE | 
       
        FILTER_VALIDATE_IP
        | 
       
         Fails validation for the following reserved IPv4 ranges: 0.0.0.0/8, 169.254.0.0/16, 127.0.0.0/8 and 240.0.0.0/4. Fails validation for the following reserved IPv6 ranges: ::1/128, ::/128, ::ffff:0:0/96 and fe80::/10.  | 
      
FILTER_FLAG_SCHEME_REQUIRED | 
       
        FILTER_VALIDATE_URL
        | 
       Requires the URL to contain a scheme part. | 
FILTER_FLAG_HOST_REQUIRED | 
       
        FILTER_VALIDATE_URL
        | 
       Requires the URL to contain a host part. | 
FILTER_FLAG_PATH_REQUIRED | 
       
        FILTER_VALIDATE_URL
        | 
       Requires the URL to contain a path part. | 
FILTER_FLAG_QUERY_REQUIRED | 
       
        FILTER_VALIDATE_URL
        | 
       Requires the URL to contain a query string. | 
FILTER_REQUIRE_SCALAR | 
       Requires the value to be scalar. | |
FILTER_REQUIRE_ARRAY | 
       Requires the value to be an array. | |
FILTER_FORCE_ARRAY | 
       If the value is a scalar, it is treated as array with the scalar value as only element. | 
| Version | Description | 
|---|---|
| 7.3.0 | 
         The explicit usage of FILTER_FLAG_SCHEME_REQUIRED
         and FILTER_FLAG_HOST_REQUIRED has been deprecated.
         | 
       
| 7.1.0 | 
         FILTER_FLAG_EMAIL_UNICODE has been added.
         | 
       
| 5.3.2 | 
         FILTER_FLAG_STRIP_BACKTICK has been added.
         | 
       
| 5.2.10 | 
         FILTER_FLAG_NO_RES_RANGE supports also IPv6 addresses.
         |