array_flip() returns an array in
flip order, i.e. keys from
trans become values and
trans's values become keys.
Note that the values of
trans need to be valid keys, i.e. they need to be
either
integer or string. A warning will be emitted if a
value has the wrong type, and the key/value pair in question
will not be
flipped.
If a value has several occurrences, the latest key will
be used as its values, and all others will be lost.
array_flip() returns FALSE if it fails.