Mailto links doesn't allow special characters.

Problem:

When we use Mailto, in the link section(e.g insert > links), if your body message have brackets, it'll render your link unusable.

Steps to reproduce:

1. Add a page.
2. Select an blank page.
3. Click in Link, then Web Link.
4. Type, for example,

   mailto:testmail@testmail.com?subject=testing \[this message is just a test\]

   In the link text field, type: test.

5. Then, click insert, save the page, and try to click on the link.
6. You'll see that is broken.

Workaround:

Instead of using brackets, use parentheses.