Atoms are special Pegex rules that represent the small pieces of text that you can use to build up regular expressions. Usually they are one or two characters.
It may seem like a waste of time to specify
<COLON> in a regex, instead of a simple
:. There are three reasons this is encouraged. First is that you are defining a grammar for a new language, and it is worth the time to be clear and verbose. Second, using an abstraction like this can help with portabiliity to languages with different regex engines. Finally, it makes the grammar for Pegex so much simpler, because a
/ is always a part of the Pegex syntax, and a
<SLASH> is part of your grammar.