24. Metacharacters - Quantifiers: Intervals

• Be careful with intervals! Just like negation of a character class is matching a character that's not in the class, and not a magical "it doesn't matter if there's something there or not", so to is the following a little different to what we might expect:

    a{0, 0}
          

• This means that the character "a" should match a minimum of zero times (or, if you like, there is no requirement to make a match), and that there should be a maximum of zero of them - in other words, don't even bother trying to make a match. The net result is that adding an interval like this has no effect on the rest of the regex!
• It is not the same as saying that there must not be an "a" in this location.