Flag¶

A flag is another name for an option. Often, flags are booleans: they are either on, or off.

Flags are often consecutive powers of 2, so they can be merged together by addition + or by logical or |, and passed as one.

Example of flags:

preg_match(), 4th argument: PREG_OFFSET_CAPTURE and PREG_UNMATCHED_AS_NULL;
json_decode(), 4th argument: JSON_BIGINT_AS_STRING, JSON_INVALID_UTF8_IGNORE, JSON_INVALID_UTF8_SUBSTITUTE, JSON_OBJECT_AS_ARRAY, JSON_THROW_ON_ERROR;
ArrayObject::setFlags(), 1rst argument: ArrayObject::STD_PROP_LIST or ArrayObject::ARRAY_AS_PROPS.