On many wikis, protected templates have a doc subpage so that everyone can edit the documentation.

However, the [edit] section button does not appear on a sub page of a protected page because all section edit links are disabled on a protected page, regardless of the source of the text, including transclusion.

This is an important feature because it allows new users to understand that they can modify the documentation even if the template is protected.

The reverse also exists, an unprotected page that contains a protected page will have the [edit] section links. (see an example)

See also this topic on frwiki

Thank you in advance,