[PHP string] this is a magical problem today. please help me.

[PHP string] an amazing problem today. please help me with error 1:

Echo 'echo $ rst4 [$ I] ["tb_restore_content"]:
'; Echo $ rst4 [$ I] ['TB _ restore_content']."

"; Echo 'echo $ rst4 [$ I] [" tb_restore_content "] content:
'; Echo'[Reply: sasasa][Reply: sasasa] 0
1
2 ';

Running result

Some labels are not parsed when the variable a is output directly. because double quotation marks are added to it, the following error occurs:
Error 2

echo is_string($rst4[$i]['tb_restore_content']);echo "$rst4[$i]['tb_restore_content']";

Result

Reply to discussion (solution)

Why? Can't you see why?

It's amazing!
The magic of Error 1 is that you didn't clarify the problem
For error 2, the magic is that you did not follow the php writing rules
Echo "$ rst4 [$ I] ['TB _ restore_content ']";
Ying writing
Echo "{$ rst4 [$ I] ['TB _ restore_content ']}";
Or
Echo $ rst4 [$ I] ['TB _ restore_content '];

It's amazing!
The magic of Error 1 is that you didn't clarify the problem
For error 2, the magic is that you did not follow the php writing rules
Echo "$ rst4 [$ I] ['TB _ restore_content ']";
Ying writing
Echo "{$ rst4 [$ I] ['TB _ restore_content ']}";
Or
Echo $ rst4 [$ I] ['TB _ restore_content '];

Yes, I haven't noticed it for a while.

Why? Can't you see why?

Error 2: As you said, Error 1 indicates that a string contains tags, but it is not parsed when I output this variable,

It's amazing!
The magic of Error 1 is that you didn't clarify the problem
For error 2, the magic is that you did not follow the php writing rules
Echo "$ rst4 [$ I] ['TB _ restore_content ']";
Ying writing
Echo "{$ rst4 [$ I] ['TB _ restore_content ']}";
Or
Echo $ rst4 [$ I] ['TB _ restore_content '];

Error 2: As you said, Error 1 indicates that a string contains tags, but it is not parsed when I output this variable.

Then, describe the problem carefully.
If variables are involved, the values of the variables must be given separately.

It's amazing!
The magic of Error 1 is that you didn't clarify the problem
For error 2, the magic is that you did not follow the php writing rules
Echo "$ rst4 [$ I] ['TB _ restore_content ']";
Ying writing
Echo "{$ rst4 [$ I] ['TB _ restore_content ']}";
Or
Echo $ rst4 [$ I] ['TB _ restore_content '];

Error 2: As you said, Error 1 indicates that a string contains tags, but it is not parsed when I output this variable.

0

Then, describe the problem carefully.
If variables are involved, the values of the variables must be given separately.

For example

$ A ='
[Reply: sasasa] 0
2'

Echo $ a outputs a string that is not parsed, or, p or p.

Echo'
[Reply: sasasa] 0
2'

Then there is no problem

Is there anything wrong?