| ID | Used with | Description |
|---|---|---|
| FILTER_FLAG_STRIP_LOW | FILTER_SANITIZE_ENCODED, FILTER_SANITIZE_SPECIAL_CHARS, FILTER_SANITIZE_STRING, FILTER_UNSAFE_RAW | Strips characters that has a numerical value <32. |
| FILTER_FLAG_STRIP_HIGH | FILTER_SANITIZE_ENCODED, FILTER_SANITIZE_SPECIAL_CHARS, FILTER_SANITIZE_STRING, FILTER_UNSAFE_RAW | Strips characters that has a numerical value >127. |
| 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_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, 192.0.2.0/24 and 224.0.0.0/4. This flag does not apply to IPv6 addresses. |
| 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. |