regex - zero width token? -

I want to ask a very basic question about tokens, while reading about regex, book tag carat (^ ) As zero width token, can you please tell me what does it mean by zero width?

This means that it consumes without any characters. This is just a permanent claim ("should be at the beginning of the line") Another example is the front-and-back claim of zero-width claim. For example, Pearl corresponds with regex / abc (? = 123) / sequence ABC , then this sequence is done after 123 But it does not actually use 123 .