| 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 NULLfor 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 | 
|---|---|
| 5.3.2 | FILTER_FLAG_STRIP_BACKTICKhas been added. | 
| 5.2.10 | FILTER_FLAG_NO_RES_RANGEsupports also IPv6 addresses. |