Php string has a length, but the content is blank?

PHP, see the figure. the string length is 413, but the content is blank '? Why?

PHP, see the figure. the string length is 413, but the content is blank '? Why?

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PHP, see the figure. the string length is 413, but the content is blank '? Why?

 ';}?>

Check out what the asc Code corresponds to and you will know what it is.

It really has nothing to do with \ 0. Or the invisible characters. Only an empty box is displayed.
\ T \ n \ r will have this effect, but this effect will show a space in double quotation marks ""
And \ f \ 1 \ 2 \ 3 \ 4 \ 5 \ 6 \ 7 \ 0, are not even space, that is ""
Double quotation marks harm

What is this string? If it cannot be pasted, it is either a Null string, \ r \ n \ t is possible.

                                         
                                    
Most of them contain "\ 0"
$s="\0aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa";var_dump($s);
                                        
                                    
When HTML is displayed, consecutive spaces are merged into one
You can view the source code in a browser,
Chrome simply adds view-source in front of the address bar.
view-source:http://......