Question
========
Enter _any_ valid (syntactically correct) e-mail address.

Solution
========
An e-mail address consists of a local-part, followed by the @ symbol,
and a domain name. The local part may use latin letters (upper- and/or
lower-case), numbers, and certain symbols like a . or _ etc. The domain
name also allows numbers and letters but fewer symbols and needs to have
a . separating the top-level domain.

The regular expression used for validation is:

```
^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\\.[a-zA-Z]{2,}$
```

which covers the most important (but not quite all) rules that an e-mail
address has to satisfy. For more details see <https://en.wikipedia.org/wiki/Email_address>.

Meta-information
================
exname: E-mail address validation via regex
extype: string
exsolution: ^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\\.[a-zA-Z]{2,}$
