Capital Letter

How important is a capital letter?  It depends on the context, but in many locations it is very important.  Case in point, today I was developing a PHP based application and one little capital letter was breaking the whole system.  In PHP and many other programming languages capitalization plays an important role in defining different variables and options.  For example "spaceTime" and "spacetime" are not the same as far as the code is concerned.  If you set "spaceTime" to one and try to read "spacetime" later, it may not equal one.  I guess it makes sense, PHP is a programming language much like any other language in that it is used to communicate.  It is communication between human and machine. Sometimes a capital letter provides for a cleaner communication, other times it changes the whole meaning.