What is the significance of the syntax error: unexpected '.' in PHP code and how can it be resolved?

The significance of the syntax error "unexpected '.'" in PHP code is that it indicates a misplaced or unnecessary period (.) in the code. This error commonly occurs when trying to concatenate strings using the period operator (.) but forgetting to include a variable or string on one side of the period. To resolve this issue, carefully check the line where the error occurs and ensure that the period is used correctly for concatenation.

// Incorrect usage of period operator causing syntax error
$variable = "Hello" . . "World";

// Corrected code by removing the unnecessary period
$variable = "Hello" . "World";