I'm reading a book about PHP, and about using
In fact, the lowercase versions are more stable, because PHP does not
allow you to redefine them; the uppercase ones may be redefined
Boolean true is defined as case-insensitive constant, with
true being the default notation.
define("true", 1, 1);
That means it will work in any other casing as well, be it
What your book alludes to is redefining the constant in another case variant again. Which you can. All but the lowercase
true are open spots in the constant lookup table.
define("True", 2) it will take precedence over the lowercase-defined
true which would substitute for the other cases else.
It's pointless advice from your book anyway. Even though you could declare a dozen variants for the boolean constants, nobody actually does that. The presumed "more stable" reasoning is practically bogus. Prefer the notation that's more readable or matches the existing coding style.