Questions about echo

Q: & lt ;? Phpecho & nbsp; phpinfo ();? & Gt; and & lt ;? Phpphpinfo ();? & Gt; what is the difference? The second question: Is echo a function? Why does the output contain no parentheses? Questions about echo with or without parentheses.
First question:
Echo phpinfo ();
?>
And
Phpinfo ();
?>
What is the difference?

The second question: Is echo a function? Why does the output contain no parentheses? What is the difference between parentheses and parentheses?
Please give me a detailed explanation of echo usage and online answers. thank you, echo.
------ Solution --------------------
Take a closer look at phpinfo:
In addition to the php configuration information, this function returns the success/failure flag: TRUE if the function is successful, and FALSE if the function fails.

Therefore, phpinfo () outputs php configuration information.
Echo phpinfo () not only outputs php configuration information, but also outputs 1 (if successful) on the page ).

That is to say, if it is only used to view the configuration information of php, both can be used.