A piece of code does not quite understand

A piece of code does not quite understand 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. I don't understand.

Reply to discussion (solution)

Wrong,
Echo"
Last file modification time ". date (" Y-m-d H: I: s ", $ file_info ['mtime']);

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.

Wrong. The brackets should not exist.

Wrong. The brackets should not exist.

Wrong. The brackets should not exist.

Your code:. date ("Y-m-d H: I: s)", $ file_info ['mtime']);
Change to. date ("Y-m-d H: I: s", $ file_info ['mtime']);

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.

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']);

Discussion triggered by a careless person

Thank you! you have learned a lot at the beginning.