Blogslug custom token

I am studying the blogslug Custom Token to better understand the regular expressions used in the example version.

And just have a couple of questions to help me understand how it works. They're regular expression questions rather than Perch questions really.

In the example:

'blogslug' => '[1-2][0-9]{3}\-[0-9]{2}\-[0-3][0-9]-[a-z0-9\-]+',

is used for the standard slug for Blog, like this

2014-12-01-christmas-is-near

As I read through the regular expression it seems to make sense when comparing it to the slug, but after the part that defines the date there is a - (dash) shouldn't that be escaped with a \ (backslash)? i.e.

'blogslug' => '[1-2][0-9]{3}\-[0-9]{2}\-[0-3][0-9] (backslash here to escape this dash) -[a-z0-9\-]+',

And what does the + signify at the end?

Thanks for any help in understanding.