Why am I not able to match multiple lines with this regex on rubular?

I'm working with the following regex (taken from the devise.rb file that devise generates):

\A[^@\s]+@[^@\s]+\z

Usually, when I'm learning about a regex I use rubular. For example, if I wanted to learn about the regex /.a./, I would set up my workspace as shown here:

Notice how I'm using multiple examples:

foo
bar
baz

And rubular is giving me feedback that both bar and baz match.

Now I'd like to learn about the regex that devise generates: /\A[^@\s]+@[^@\s]+\z/. So I set up my rubular workspace as shown here here:

There isn't a match. It's because I have two examples:

foo@foo.com
cats@cat.com

But I was expecting them both to match. Why aren't both test strings matching?

This is because the regex /\A[^@\s]+@[^@\s]+\z/ is matching the start of the string with \A and end of the string with \z.

If you remove both \A and \z and instead try to match /[^@\s]+@[^@\s]+/ then it will match both email addresses as shown here:

Also, it's worth mentioning that the start and end of a string is different from the start and end of a line. Each are represented by four different patterns shown below and also on rubular in the Regex quick reference:

^   - Start of line
$   - End of line
\A  - Start of string
\z  - End of string

There can be multiple lines in a string; however, a single string goes from \A to \z. So to continue with this multiple email example. Replacing the start and end of a string patterns with the start and end of a line patterns to get: /^[^@\s]+@[^@\s]+$/ will also match, shown below and on rubular: