Placeholder.
=:[<whitespace>]<URL>[<whitespace><USER-FRIENDLY LINK NAME>]
A prompt line should be treated the same as a "=>" link line, except that the client should prompt the user to define data to include as the [data-block] before sending the request. The precise UI for data input is not mandated, but some possible forms might include a text box widget or a file picker widget.
Per Spartan Specification (Accessed Dec 21, 2022 1846 EST)
Spartan: spartan://spartan.mozz.us/specification.gmi
Gemini: gemini://spartan.mozz.us/specification.gmi
% gem_header 20 text/gemini