Php trim deletes space characters and specified characters

I didn't see the trim function before. I thought it could only delete the blank space. Today I found that it can also delete ""-null.
"T"-tab
"N"-new line
"X0b"-vertical list operator
"R"-Press enter
""-General white space characters
And user-specified characters.

<? Php Tutorial

Definition and usage
The trim () function removes spaces and other predefined characters from both ends of the string.

Optional. Specifies the string to be converted. If this parameter is omitted, all the following characters are deleted:
""-Null
"T"-tab
"N"-new line
"X0b"-vertical list operator
"R"-Press enter
""-General white space characters

$ Str = "this line containstliberal rn use of whitespace. nn ";

// First remove the leading/trailing whitespace
// Remove the start and end spaces.
$ Str = trim ($ str );

// Now remove any doubled-up whitespace
// Remove the blank space crowded with other items
$ Str = preg_replace ('/s (? = S)/', '', $ str );

// Finally, replace any non-space whitespace, with a space
// Finally, remove the non-space blank and replace it with a space.
$ Str = preg_replace ('/[nrt]/', '', $ str );

Echo "<pre >{$ str} </pre> ";

//

<? Php
$ Str = "## remove specific characters at both ends of the string using the trim function ####";
$ Str1 = trim ($ str, "#"); // input the second parameter for the trim function. trim deletes the # Characters at both ends of the string $ str.
Echo $ str. "<br> ";
Echo $ str1;
?>

?>