Variables are used for storing values, such as numbers, strings or function results.
All variables in PHP start with a $ sign symbol.
The script shows the variable type can be changed while program executes.
   
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To concatenate two or more variables together, use the dot (.) operator.
The script shows variables do not need to be strings.  
They could be integer or real numbers or others. 
   
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a-Z, 0-9, and _ ).
 $my_string or with capitalization such as $myString.