^[0-9]{1,2}$

We are introducing a new syntax element; the curly braces. This allows us to specify certain numerical combinations of the previous expression. The simplest of these is {n} where n is the number of times the expression is applied. You can though use combinations like {n,n+1) to denote more than one numerical match condition.

So imagine you were looking for any number between 0 and 99999, you could represent it this way:

^([0-9]|[0-9][0-9]|[0-9][0-9][0-9]|[0-9][0-9][0-9][0-9]|[0-9][0-9][0-9][0-9][0-9])$

or you could represent it this way:

^[0-9]{1,5}$

Which I think is more human readable.

It also offers certain flexibility.

Imagine you wanted numbers that contained leading zeroes between 00000 and 99999. You could then manipulate the expression:

^[0-9]{5}$

So when learning regular expressions, while simple syntax is good, a fuller understanding of the syntax can lead to SIMPLER regular expressions.