PHP output variable enlarges bracket {} function

PHP output Variable increase bracket, what is this writing? Look at the following code: [PHP] <?php header ("content-type:text/html;   Charset=utf-8 ");   $test = "1 variable 1";   echo "preceded by a String AA". $test. "BB Back string";   echo "preceded by a string AA {$test} bb back string"; ?> can see that PHP output variable braces are used with the. Operator output variable string effect is the same, summed up the following 3 points to help understand the PHP output variable to increase the parentheses {} function: 1. Represents a variable in {}, which is handled according to the variable when executed; 2. Refers to the special inclusion of variables used in strings so that you can reduce the amount of code input by not using the. operator; 3. Prevents the variable name from being linked with the following string. Attachment: The function of the brace {} in a string variable: The PHP variable is followed by a brace {}, which is filled with numbers, which refers to the character corresponding to the corresponding ordinal of the PHP variable. For example: $str = ' Hello '; echo $str {0}; Output is h echo $str {1}; Output to E If you want to check how long a string is satisfied, consider replacing the strlen function with this brace {} plus isset, because isset is a language structure and strlen is a function, so using isset is more efficient than using strlen. For example, to determine whether a string is less than 5:if (!isset ($str {5})) is better than if (strlen ($STR) < 5).