A piece of code is not clear

Echo & nbsp; "& lt; br/& gt; & nbsp; last file modification time ". date ("Y-m-d & nbsp; H: I: s)", $ file_info ['mtime']); echo & nbsp; "& lt; br/& gt; & nbsp; the code in the last modification of the file is not clear.
Echo"
Last file modification time ". date (" Y-m-d H: I: s) ", $ file_info ['mtime']);

Echo"
Last file modification time"
Add. date ("Y-m-d H: I: s)" to the end of the connection. why do we add these two double quotation marks and put the quotation marks out of the brackets. This does not understand php file io
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Wrong,
Echo"
Last file modification time ". date (" Y-m-d H: I: s ", $ file_info ['mtime']);
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Date ("Y-m-d H: I: s", $ file_info ['mtime']);
Date ("Y-m-d H: I: s)", $ file_info ['mtime']);

With an extra bracket, you can understand it after running it.
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Wrong. The brackets should not exist.
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Wrong. The brackets should not exist.
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Your code:. date ("Y-m-d H: I: s)", $ file_info ['mtime']);
Change to. date ("Y-m-d H: I: s", $ file_info ['mtime']);
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What you think you don't understand is the last thing you shouldn't understand.
If the string is not over, you cannot take it out of context.

The string can save any content, including the date format string.
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You treat date ("Y-m-d H: I: s", $ file_info ['mtime']) as a string
PHP concatenates a string with a dot (.)

Echo"
Last file modification time ". date (" Y-m-d H: I: s ", $ file_info ['mtime']);
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Discussion triggered by a careless person