PHP has a predefined constant true whose value is the integer 1. How to understand this?

When I executed get_defined_constants(), I accidentally discovered that PHP has an internal constant with the name true and the value 1. There are also constants named false and null.
Does PHP treat true as a constant? Shouldn't it be a "value"?
Shouldn’t it be a value with data type boolean?
I tried to execute echo(true), the browser output the character 1, and when I var_dump(true), it output bool(true). Isn’t this an obvious contradiction?
Also, true===1 is not true. true==1 is established.
So I want to know how php handles true false null.

Reply content:

When I executed get_defined_constants(), I accidentally discovered that PHP has an internal constant with the name true and the value 1. There are also constants named false and null.
Does PHP treat true as a constant? Shouldn't it be a "value"?
Shouldn’t it be a value with data type boolean?
I tried to execute echo(true), the browser output the character 1, and when I var_dump(true), it output bool(true). Isn’t this an obvious contradiction?
Also, true===1 is not true. true==1 is established.
So I want to know how php handles true false null.

echo input is a string, so true is type-converted. You can refer here

Printing or echoing a FALSE boolean value or a NULL value results in an empty string:
(string)TRUE //returns "1"
(string)FALSE //returns ""
echo TRUE; //prints "1"
echo FALSE; //prints nothing!

Reference documentation

Crooked building. Tell a C++ story.
Windows API has a data type BOOL, with a similar definition

typedef int BOOL;

Then there are TRUE and FALSE macros, the definitions are respectively

#define TRUE 1
#define FALSE 0

C++ itself also has a macro NULL, the definition is

#define NULL 0

And I suspect that PHP treats true as a boolean type 1. Just guessing, please feel free to object if I'm wrong.