What are the potential pitfalls of using commas to separate functions in PHP output?

Using commas to separate functions in PHP output can lead to unexpected results or errors because commas are used as separators between arguments in function calls. To avoid this issue, it is recommended to concatenate the output of multiple functions using the dot (.) operator instead of commas.

// Incorrect usage of commas to separate functions in PHP output
echo "Hello, " . strtoupper("world") . ", " . ucfirst("have a nice day") . "!";

// Correct way to concatenate output of multiple functions in PHP
echo "Hello, " . strtoupper("world") . ", " . ucfirst("have a nice day") . "!";