PHP variables - w3resource
Check If a Variable Is a String in PHP - Maker's Aid
Interpolating Variables in Strings | Spring Into PHP 5
Variable Substitution in PHP – BrainBell
String Compare Using == Operator and STRCMP Function in PHP | Delft Stack
PHP: Convert String to Number
Beginner guide of PHP Strings - DevOpsSchool.com
What does $$ (dollar dollar or double dollar) means in PHP ? - GeeksforGeeks
How to link string literals with variables in PHP? | Droptica
Create an object from a string variable in PHP - DEV Community
Learn PHP - Learn PHP Variables Cheatsheet - Codecademy | PDF | Integer | String (Computer Science)
PHP Variables: The Ultimate Guide - WebFX
PHP - Variable Types
String in PHP | Four Different Types of String Declaration in PHP
PHP - Concatenate string and number
Type Conversion: Convert variable data type in PHP – BrainBell
PHP String Exercise: Convert the value of a PHP variable to string - w3resource
PHP String Interpolation, Using Variables in Strings
Learn PHP Syntax, Comments, Variables and Data Types – with Examples
PHP variables with a string literal - sbsharma
The Top 9 Most Popular PHP String Functions – vegibit
Combining Strings (How To) | PHP Basics | Treehouse
php - unexplained syntax error when adding string to variable - Stack Overflow
