The strtoupper function is a built-in function in PHP that converts all characters in a string to uppercase letters.
This function will not alter numbers or special characters within the string, only converting letter characters to uppercase.
The strtoupper function is language-independent, meaning it will convert alphabetic characters to uppercase regardless of the current language environment.
This function returns the transformed string without altering the original string.
The strtoupper function is case-insensitive, meaning it can convert a string to all uppercase regardless of whether it contains lowercase letters in the original string.
