This file includes a regular expression to match numbers. This
will save quite a bit of time in places where you want to test if
something is a number without wasting the time to parse it or throw
an exception if it isn't. For example, you can call isDouble() to
see if a String is a double without having to try/catch the
NumberFormatException that gets produced if it is not.
The regular expression is conveniently provided in the javadoc for Double.