Why must variable names in PHP begin with a letter or underscore, but not a number?

Variable names in PHP must begin with a letter or underscore because PHP variable names cannot start with a number. This is a syntax rule in PHP to differentiate variables from numerical values. To solve this issue, always ensure that variable names start with a letter or underscore when declaring them in PHP. 

// Incorrect variable name starting with a number
$1variable = "Hello World";

// Correct variable name starting with a letter
$variable1 = "Hello World";

Keywords

variable names PHP underscore letter number

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