How does PHP determine if 0.0/0.00/0.000 is empty? Test the empty function.

if $number = =0     )echo ' empty '; if Floatval ($number) = = 0    )echo ' empty '

First, PHP thinks that 0.0 is empty, so 0.00 and 0.000 will also be considered null as 0.0, so empty will return true to express PHP's rules.
However, in the world of PHP, ' 0.0 ', ' 0.00 ', and ' 0.000 ' are not considered null, so empty will return false.
Thus, the landlord said the "elegant judgment 0.0/0.00/0.000 is empty" refers to what kind of situation? How can the empty function be incompetent?
(add: The empty function only accepts variables)

How does PHP determine if 0.0/0.00/0.000 is empty? Test the empty function.