Questions about the use of single and double quotation marks for strings

Question about using single quotes and double quotes for strings $ pattern_title & nbsp; = '/& lt; TITLE & gt ;(.*?) & Lt; \/TITLE & gt;/iU '; // define a regular expression to obtain the TITLE of a webpage $ result = file_get_contents ($ url ); preg_match_all ($ pattern_t about the single and double quotation marks used for strings
$ Pattern_title = '/ (.*?) <\/TITLE>/iU '; // defines a regular expression to obtain the TITLE of a webpage. <br/> $ result = file_get_contents ($ url ); <br/> preg_match_all ($ pattern_title, $ result, $ title); <br/> The problem is that, in single quotes, it is not necessary to transfer '\' and, how can I add '\' before '/'? <br> ------ solution -------------------- <br> to write it, so you don't need to <br/> '# <TITLE> (. *?)# IU'
Do you understand? If it is not escaped, how do you identify the three delimiters in php?
------ Solution --------------------
Escape any ambiguity