Description for Contact link in custom profile fields

Custom profile fields can be displayed as contact field. When doing so, two additional fields "Contact description" and "Contact link" are available for configuration.

The field "Contact link" can contain variables (e.g. %s in https://www.icq.com/people/%s/ ). There is no description about variable usage available.

A description about variable usage should be given in FIELD_IS_CONTACT_EXPLAIN or somewhere else