ereg_replace(): ereg_replace() function is case sensitive.
eregi_replace(): eregi_replace() function is not case sensitive. 

Ans: Property overloading continues to protect properties by forcing access and manipulation through public methods, yet allowing the data to be accessed as if it were a public property

The explode() function splits a string into a series of substrings, with each string boundary determined by a specific separator.
 
Its prototype: explode(string separator, string string [, int limit]).

Passing arguments by value: 
Means any changes made to those values within the scope of the function are ignored outside of the function.
Passing arguments by reference: 
Means any changes made to those values within the scope of the function are reflected outside of the function.

:: operator is used to access static methods that do not require object initialization.